Heads Above The Rest!; Exploring The Science and Art Of The Equine Head for Sculpting: Part 11

Introduction

Welcome back to this series discussing the equine head from an anatomical, evolutionary, and artistic point of view. We’ve learned quite a bit so far, but we have more to go—there really is a lot to something that seems so simple, isn’t there? Biology is a complicated, messy thing, and everything is symbiotic and interdependent, so to understand one feature means we need to understand all the others. This is particularly true of the equine which evolution has shaped into what’s purely functional with great economy of form and function. In few other animals is so much done with so little. And it’s in the equine head where we see this efficiency so clearly and profoundly expressed. So let’s continue with our exploration with the last of his fascial muscles…

More Muscles

Muscles Of The Tongue

The tongue is the largest muscle in the horse’s head, and while myriad little muscles and fleshy bits related to it are present, we’ll only deal with the primary muscles, as follows:

• Lingualis proprius: The tongue itself, the root (radix linguæ) is attached to the Hyoids, soft palate, and the pharynx. Only the upper portion is free, and the root and lower portion are attached to the floor of the mandible. Comprised of longitudinal, transverse, and perpendicular muscle bundles, it’s the largest muscle in the head. Its simultaneous stiffening of its muscle bundles stiffens the tongue. Blood is supplied by the lingual artery and sub-lingual branches of the external maxilllary artery, and nerve impulses are supplied by the lingual, glosso-pharyngeal, and hypoglossal nerves.
• Styloglossus (also can be written Stylo-glossus): A long, thin muscle that lays along the lateral portions of the tongue. It originates on the lateral surface of the stylohyoid bone, near their articulation the keratohyoid bones, and inserts near the tip of the tongue, blending with its twin from the opposite side. Its dual action pulls the tongue up and back while its single action pulls the tongue to the side and up. The lingual artery supplies blood and the hypoglossal nerve provides nerve impulses.
• Hyoglossus (also written Hypo-glossus): A wide, flat muscle that’s a bit thicker than the Styloglossus. It lays on the lateral portions of the root and body of the tongue, partly covering the Styloglossus. Its fibers pass obliquely upwards and forwards, towards the median plane of the dorsal tongue. Its origin is the lingual process of the basihyoid bone, and the stylohyoid and thyrohyoid bones, and its insertion is the muscle body of the tongue; most fibers are near the median dorsal plane. Its dual action pulls the tongue down and back while its single action pulls the tongue to one side, down and back. Blood is supplied by the lingual artery, and nerve impulses from the hypoglossal nerve.
• Genioglossus (also written Genio-glossus): A fan-shaped muscle, laying parallel to the median plane of the tongue. Its origin is the medial surface of the mandible, just behind the symphysis; some fibers fan to the tip, some to the dorsal tongue and some to the root, and some even pass to the keratohyoid bones. It inserts on the tip and root of the tongue, fanning sagittally into it. Its dual action depresses the tongue and helps to form the dorsal groove when both muscles act. However, it also pulls the tongue forwards or backwards and down, depending which fibers are activated. Its single action moves the tongue to one side, either forwards or backwards. The lingual artery supplies blood and the hypoglossal nerve provides nerve impulses.

Muscles Of The Hyoid Apparatus

There are many muscles involved with swallowing, but the primary ones that activate the Hyoids are, as follows:

• Digastricus (already described)
• Mylohyoideus (also written mylo-hyoideus): With its twin, they form a sling to support the tongue within the free span of the mandible. It originates on the inner alveolar ventral surface of the mandible, and inserts by a fibrous median raphe to the symphysis of the basihyoid and to the lingual process on the basihyoid. It raises the floor of the mouth, tongue and Hyoids. The sublingual artery supplies blood and the mylohyoid nerve (from the mandibular nerve) supplies nerve impulses.
• Stylohyoideus (also written Stylo-hyoideus): A slender, fusiform muscle running at an almost parallel angle to the stylohyoid bone, it originates on the muscular process of the stylohyoid bone, and inserts on the thyrohyoid bone with its tendon encircling the round tendon of the Digastricus. It works to draw the tongue, larynx, and Hyoids upwards and backwards. Blood is supplied by the external carotid artery, and nerve supply from the facial nerve (from the stylo-hyoid branch).
• Occipitohyoideus (also written Occipito-hyoideus): A small triangular muscle, it lays between the top of the stylohyoid bone and the paramastoid process. It originates on the paramastoid process of the occipital bone, and inserts on the back and lower rim of the stylohyoid bone. It pulls the Hyoids backwards. Blood is supplied by the occipital artery, and nerve impulses form the facial nerve. 
• Geniohyoideus (also written Genio-hyoideus): A long round muscle, it lays under the tongue next to its twin. It arises from a short tendon and its belly is comprised of long bundles of parallel muscle fibers. It helps to form the muscular basis of the oral cavity. Its origin is the medial surface of the ramus, from a small depression near the symphysis, and its insertion is the lingual process of the basihyoid bone. It pulls the tongue, larynx and Hyoids forwards. The sublingual artery is its blood supply and the hypoglossal nerve provides nerve impulses. 
• Keratohyoideus (or also called Ceratoyhoid muscle, Ceratohyoideus, or also Kerato-hyoideus): Another small triangular muscle laying between the Keratohyoids and the Thyrohyoids. It originates on the back of the keratohyoid bones, the rostral border of the thyrohyoid bone, and the surrounding portion of the ventral rim of the stylohyoid bone. It inserts on the dorsal edges of the thyrohyoid bones. In action, it raises the thyrohyoids and the larynx. Blood is supplied by the lingual artery, and nerve supply from the glosso-pharyngeal nerve. 
• Hyoideus transverses: A small singular muscle that attaches between the keratohyoids. When contracted, it raises the root of the tongue; when relaxed, it remains slack. Blood is supplied by the lingual artery, and nerve impulses by the glosso-pharyngeal nerve.
• Sternohyoideus: It’s divided mid–neck by a transverse tendinous intersection that separates it into cranial and caudal parts. It originates on the manubrium of the sternum, and inserts on the linguinal process of the basihyoid bone. It retracts and depresses the Hyoids and the base of the tongue. The common carotid artery supplies blood and the ventral branch of cervical nerve, 1 and 2 are its nerve supply.
• Sternothyrohyoideus (also written Sternothyro-hyoideus ): A long slender digastric muscle running below the trachea; sometimes regarded as a muscle of the neck. Sometimes its rostral continuation is considered a separate muscle, the Thyrohyoideus. Like the Sternohyoideus, it’s also divided mid–neck by a transverse tendinous intersection that separates it into cranial and caudal parts. It originates on the manubrium of the sternum, and inserts on the basihyoid (its lingual process) and the thyroid cartilage of the larynx. In action, it depresses and pulls backwards the Hyoids, tongue and larynx; when the depressor muscles of the tongue are contracted, the Sternothyrohyoideus may also fix the Hyoids for the sucking mechanism. Blood is supplied by the common carotid artery, and nerve supply from the ventral branch of cervical nerve, 1 and 2.
• Omohyoideus (or Subscapula-hyoidens) : A thin fleshy muscle, it forms the floor of the jugular groove of the neck. It originates on the subscapular fascia near the shoulder joint, and inserts on the lingual process of the basihyoid bone. It pulls back the Hyoids and tongue. The common carotid artery and superficial cervical artery supply blood and the ventral branch of the first cervical nerve provides nerve impulses.

Cutaneous Muscles

The head has important cutaneous muscles, or bundles of tiny muscles embedded in the superficial fascia. Because these cutaneous muscles lay within the fascia of the skin, they have little or no attachment to the skeleton. These facial cutaneous muscles run from the larynx to the mouth and move the facial skin while helping to retract the mouth. They become very thin around the orifices and blend with the periosteum on the nasal and frontal bones. Specifically, the head has two primary cutaneous muscles:

• The cutaneous fasciei: Thin and typically incomplete muscular layer, it sweeps over the mandibular space and the masseter muscle. One branch runs to the angle of the mouth and blends with the orbicularis oris. This part becomes…
• The cutaneous labiorum (also called the retractor anguli oris): An extension of the cutaneous fasciei and helps to pull up the angle of the mouth.

Conclusion To Part 11

Phew! That was a lot to wade through, wasn’t it? Extra points for sticking around! Now it may seem like overkill to have gone into such detail, but the truth is we need to know just how complex the equine head truly is if we’re going to fully appreciate it. That is to say, it's quite different to look at the horse's head with "conventional" eyes than it is to perceive it with penetrating ones. The typical would have us see the head with a more superficial perspective, focusing more on breed type and "beauty" than anything else. This is fine, but only if we have a biological perspective, too. Indeed, it's this view of the head that gifts us with context, of the organic parameters that determine its shape and function. If our choices aren't seated in biological context first then, we risk not only misinterpreting breed type, but distorting it into nonviable forms. We also may miss subtleties of expression and gesture intrinsic to equine communication and personality, or even create errors when it comes to gender, age, and species' differences. So much is going on in any given second, we need to be hyper–aware of all these little tweaks that will influence its nature and features. Truly, being able to See the equine head with a diagnostic view can help us in so many ways beyond simply capturing its innate beauty. So until next time…heads up for Part 12!

“I obliged myself to explore where I might otherwise not have. And that’s what ‘mind-flexing’ is all about – making those brain-muscles work so that you feel empowered to pursue your own vision.” ~ Tony Smibert

Heads Above The Rest!; Exploring The Science and Art Of The Equine Head for Sculpting: Part 10

Introduction 

Hello again! Welcome back to this analytical and artistic series about the equine head. We’re currently discussing head musculature, those fleshy bits that provide so much shape and expression to equine cranial topography. Head musculature is a common site of error in sculpture, and for good reason—it’s quite complicated despite its apparent simplicity. It's actually unlike the musculature of the body since its so interwoven between deep and superficial layers, it's rather deceptive. This means we need a good grasp of its features if we hope to recreate a convincing head in clay so we need both an anatomical and artistic understanding as one informs the other. So to continue our exploration, let’s keep going!…

More Muscles

Muscles Of The Upper Face And Mandible

• Masseter, deep layer: This powerful muscle that, together with the superficial layer, forms an obvious fleshy mass on the ramus. It’s comprised of two main parts, a superficial layer and a deep layer, though the two are largely fused except around their origins and insertions; both are pennate muscles. It originates via a strong tendon by the zygomatic arch and down the masseteric ridge to insert on the outside surface of the ramus. A small portion is visible (and therefore superficial) beneath the superficial portion. Its dual action closes the mouth in conjunction with the Temporalis and Pterygoideus muscles. Its single action helps with the lateral and rotary motions of the jaw. Blood is supplied by the transverse facial and masseteric arteries, and nerve supply from the mandibular nerve.
• Masseter, superficial layer: This powerful muscle that, with the deep layer, helps to form the obvious fleshy mass on the ramus. It’s comprised of two main parts, a superficial layer and a deep layer. The superficial layer is covered by a strong aponeurosis and tendinous intersections divide it into layers. Its muscle bellies are rather distinct, and can be seen when the horse is chewing or tense (as to clench his jaw). It originates mostly along the masseteric ridge and inserts on the outside surface of the ramus. Its dual action closes the mouth in conjunction with the Temporalis and Pterygoideus muscles. In single action, it helps with the lateral and rotary motions of the jaw. Blood is supplied by the transverse facial artery, and nerve supply by the mandibular nerve.
• Temporalis: Laying inside the temporal fossa, it’s covered by a strong aponeurosis and has strong tendinous striations within its muscle belly. Its thickness around its origin is rather thin, but as it approaches its insertion, it becomes nearly one inch thick. It helps to form the “Salt Cellar” by its frontal, orbital, and zygomatic portions to the attachment at the coronoid process. It originates on the rough areas and crests of the temporal fossa and the medial surface of the zygomatic arches, and inserts on the mandible’s coronoid process, covering it and the front rim of the vertical ramus of the maxilla, fusing partly with the masseter. Its dual action closes the mouth whereas in single action, it helps with lateral and rotary motions of the jaw. Blood is supplied by the superficial and deep temporal arteries and the posterior meningeal artery, and nerve supply by the mandibular nerve.
• Pterygoideus medialis (also called the Medial pterygoid, or Taragoideus): It lays on the medial surface of the ramus like an internal mirror to the masseter (which lays on the other side of the ramus). It’s the larger portion of the two muscles and its muscle fibers are mostly vertical with a lot of tendinous tissue (septa). It originates on the crest of the pterygoid processes of the basisphenoid (sphenoid) and palatine bones, and inserts on the large concave inner surface of the ramus and mandible and the medial rim of its ventral border. Its dual action aids the Masseter to clamp the jaw, and in single action helps to produce lateral jaw motion, or rotary chewing motion. Blood supply comes from the maxillary and inferior alveolar arteries, and nerve supply from the mandibular nerve.
• Pterygoideus lateralis (also called the lateral pterygoid, or Taragoideus): Much smaller though fleshier than the Pterygoideus medialis that it overlays (the mandibular nerve lays between these two muscles). Its muscle fibers are more downward and backward, longitudinally. It originates from the sides of the pterygoid process of the basisphenoid (sphenoid) bone, and inserts on the medial surface of the mandible and the mandible’s condyle. In dual action it draws the mandible forwards, and in single action it moves the mandible laterally, to the side opposite the acting muscle (because the origin of both muscles is closer to the media plane). Blood is supplied by the maxillary and inferior alveolar arteries, and nerve impulses from the mandibular nerve.
• Occipito mandibularis (also written as Occipitomandibularis, or the Occipitomandibular muscle): A short, fusiform muscle with a lot of tendinous tissue within its muscle belly. It blends with the posterior belly of the Digastricus muscle (and often considered another belly of that muscle). It originates on the paramastoid process of the occipital bone (in common with the posterior belly of the Digastricus). It inserts on the posterior rim of the ramus; covered by the parotid gland. Its dual action helps to open the mouth by pulling on the lower jaw while its single action helps to draw the mandible laterally and help with rotary action. Blood is supplied by the external carotid and sublingual arteries, and nerve impulses by the facial nerve.
• Digastricus: A unique muscle with two flat fusiform bellies with a round tendon down the middle (the tendon has a synovial sheath). The anterior belly is larger than the posterior belly. It originates on the paramastoid process of the occipital bone (sharing an insertion with the occipito mandibularis), and inserts through the fork of the Stylohyoideus onto the medial and ventral portion of the ramus, in the molar region. It helps to close or open the jaw. If the jaw is closed, the bellies of this muscle raise the Hyoids and tongue, helping to create the swallowing mechanism. Blood is supplied by the external carotid and sublingual arteries, and nerve impulses from the facial and mandibular nerves.

Muscles Of The Muzzle And Mid–face

• Levator labii superioris (or Levator labii superioris proprius): A thin muscle with a distinct muscle belly and a long tendon. The muscle belly starts flat at first, but narrows and thickens to taper off into a long thin tendon, which joins its twin over the alar cartilages of the nostrils and forms a common band with spreads over the upper lip. Its origin is where the lacrimal, malar and maxilla bones join together and it flows forwards alongside the nasal bones and above the nostril to join its pair between the nostrils to form a common tendon which crosses over the Transversus nasi to blend into the upper lip. It either raises the lips or draws them side to side.
• Zygomaticus: A superficial slender, thin strap–like muscle. It originates from the fascia of the Masseter, underneath the masseteric ridge (teardrop bone), inserting on the corner of the mouth to blend with the Buccinator. Working together with its pair, it pulls the corners of the mouth backwards and upwards. By itself, it pulls a corner of the mouth backwards, towards the eye, and upwards. It gets its blood supply from the facial artery and nerve impulses from the facial nerve.
• Incisivus superior (or Incisivus superioris): It originates at the alveolar border along the ventral ridge of the premaxilla from the second incisor to the second premolar, laying beneath the mucous membrane of the upper lip. It inserts with the upper lip, and pulls it down. Blood is supplied by the facial artery and nerve impulses come from the facial nerve.
• Incisivus inferior (or incisivus inferioris): Lays underneath the mucus membrane of the lower lip and is similar to the Incisivus superior. It originates from the alveolar border of the mandible from the second incisor to near the second premolar and inserts on the skin of the lower lip and the chin. With its pair, it lifts the lower lip, but by itself it lifts only one respective side. However, with the Incisivus superior and the Orbicularis oris, the upper and lower lips are pursed together such as to snatch food and pull it towards the incisors. It gets its blood supply from the facial artery and innervation from the facial nerve.
• Mentalis (or the mental muscle): Located within the chin, it’s heavily invested with fat and connective tissue making it very flexible and squishy. With its pair, it tenses the chin and by itself it lifts and pulls the chin to one side. It originates from the mandible to insert into the chin skin. It gets its blood supply from the mental artery and nerve impulses from the mental nerve.
• Depressor labii inferioris: A thin, slender muscle ventral to the Buccinator (and sometimes fused to it as far back as the second premolar), this muscle arises from the alveolar border of the ramus near the coronoid process and the maxillary tuberosity. Flowing below the Buccinator it becomes rounded and inserts on the lower lip with a tendon, blending with the Orbicularis oris and its pair on the other side. It pulls back the lower lip with its pair, but by itself it pulls one side of the lower lip back. It also depresses the jaw, or draws it laterally. The facial artery supplies it with blood and the facial nerve provides its impulses.
• Buccinator, superficial layer (pars buccalis or alveolo labialis): A fleshy muscle that, with its deep layer, helps to form the muscular basis of the mouth. With two heads and two bodies, the first originates above the first molar on the maxilla and over the interdental space and the second over the interdental space of the mandible. They blend together and fuse to the tendon of the deep portion of the Buccinator to blend with the Orbicularis Oris. In particular, the fibers of the top and bottom portion radiate forwards from this tendon like barbs of a feather. Together they pull back the corners of the mouth or contract them (flattening them) to push water or food back into the throat for chewing or swallowing. It also pushes food against the teeth while chewing. By itself it pulls back a corner of the mouth or contracts to manipulate food or water within the oral cavity. It gains its blood supply from the facial and buccal arteries and its nerve impulses from the facial nerve.
• Buccinator, deep layer (pars molaris or molaris): A fleshy muscle with longitudinal muscle fibers, with a paired superficial layer (above) that together form the muscular basis of the mouth. It originates by two heads on the maxilla above the last three molars and around the coronoid process and the second from just behind the last molar on the curved ramus of the mandible. They meet in a strong tendon running down its length, starting from the coronoid process and uniting with the Orbicularis oris and ventrally with the Depressor labii inferioris. By itself it pulls back the corners of the mouth or contracts (flattens) to push water or food back into the throat for chewing or swallowing, and to push food against the teeth while chewing. By itself, it pulls back the corner of the mouth or contracts to manipulate food or water within the oral cavity. It gets its blood supply from the facial and buccal arteries, and its nerve supply from the facial nerve.
• Orbicularis Oris: Described as a fleshy sphincter muscle and not attached to bone, it forms the shape of the lips with muscle fibers that run somewhat parallel to that the lips. It works to open and close the lips. It blends with the muscles that converge on it, and is embedded between the skin and mucus membranes of the lips. It’s very mobile, pliable, and stretchy. 

Muscles Of The Nostrils

• Nasal diverticulum (also called the “false nostril”): The alar fold of the comma cartilages divides the nasal cavity into a larger lower portion (which goes into the nasal cavity) and a smaller upper portion, the false nostril, which is cone–shaped and about 3–4” (7.6–10cm) long, terminating at the nasoincisive notch of the maxilla. Like the guttural pouches, this is a peculiarity to equines. Their true purpose is largely unknown, but perhaps a clue can be found in the fact that tapirs have the same structure, but in a more highly developed form, while this structure also is present in the rhinoceros. 
• Levator nasolabialis (or Levator labii superioris alæque nasi): A thin, largely subcutaneous muscle that originates by the thin aponeurosis of the nasal and frontal bones. Its thin muscle belly branches towards the nostril through the Dilatator naris lateralis. Its dorsal branch (the larger and deeper portion) blends with the upper lip and the lateral wings of the nostrils, with the Dilatator naris lateralis. The ventral branch (the smaller and more superficial of the two) blends with the Orbicularis oris. Its dual action lifts the upper lips (helping to open the mouth) and elevates or dilates the nostrils. Its single action causes a snarl and dilates one nostril. It gets its blood supply from the facial artery and innervation from the facial nerve.
• Dilatator naris lateralis (also called Caninus): A thin, triangular muscle that runs between the two branches of the Levator nasolabialis. It originates on the maxilla, near the protrusion of the masseteric ridge, and inserts through the fork of the Levator nasolabialis to the lateral wing of the nostril. Its ventral fibers blend with the Orbicularis oris. Its dual action dilates the nostrils and elevates upper lips while its single action dilates a nostril and elevates upper lip. The facial artery supplies blood and the facial nerve provides nerve impulses.
• Transversus nasi (also called Transversalis nasi, or Dilator naris apicalis, or transverse nasal muscle): An unpaired, short, thick muscle with transverse muscle fibers comprised of two portions that connect the comma cartilages of the nostrils. The dorsal portion is also called the Pars dorsalis lateralis nasi and the ventral portion also is called the Pars ventralis lateralis nasi. The muscle fibers of the thin dorsal layer arise from the nasal bone. The thicker ventral layer arises from the nasal process of the premaxilla and surrounding areas of the maxilla. The dorsal layer inserts onto the heads of the comma cartilages, effectively connecting them together. The ventral layer connects the tails of the comma cartilages together and blend with the Orbicularis oris. It dilates the nostrils by pulling the comma cartilages towards each other inwardly and their tails more vertically, when seen from the front (often seen with the blowing or snorting action). The facial and palato-labial arteries provide blood and the facial nerve provides nerve impulses.
• Lateralis nasi, dorsal part (also called the pars Dorsalis lateralis nasi or the Dilator naris dorsalis): A thin muscle sitting along the borders of the naso-maxillary notch. It originates on the nasal bone, and inserts on the parietal cartilage of the nasal bone and surrounding soft walls of the nasal cavity. A portion of its muscle fibers curve inwards to attach to the cartilaginous protrusions of the turbinate bones (mostly the ventral turbinate bone). It dilates the entrance of the nasal cavity and to helps to dilate the nostrils. Contrary to many claims, this muscle doesn’t dilate the false nostril. Instead, it activates the lateral walls of the nasal cavity by drawing it outward, which tends to constrict rather than dilate the false nostril. The facial and palato-labial arteries supply blood and the facial nerve is its nerve supply.
• Lateralis nasi, ventral part (also called the Pars ventralis lateralis nasi, or the Dilator naris ventralis): A thicker muscle laying behind the previous muscle, along the ventral rim of the naso-maxillary notch. It arises from the nasal process of the premaxilla and immediate areas of the maxilla, and its muscle fibers curve inwards to attach to the cartilages of the turbinate bones, mostly the ventral turbinate bone, while other portions attach to the entrance of the nasal cavity. A small portion runs from the “tails” of the comma cartilages to the lateral wing of the comma cartilages. It dilates the cavity of the nasal cavity, rotates the turbinate cartilages outward, and also helps to dilate the nostrils. The facial and palato-labial arteries supply blood and the facial nerve is its nerve supply.

Conclusion To Part 10

That’s a lot more to chew on, but the good news is that we’re two–thirds through his facial muscles—we’ve got just a little bit more to go! Clearly, the equine head is a complicated bit of anatomy owning to its distinct skull and the particular nature of its flesh. For this reason then, the more we understand about it, the better able we tend to become when recreating it. But sculpting the equine head isn't just a clinical exercise. There may be a degree of "connect the dots," but those dots need their own special consideration. Each individual animal has their own special orientation of those dots, for example, making his face as unique as our own. We also can't forget points of type or typical characteristics of a gene pool, both of which have important influences on cranial structure. There's also expression to consider since it can have substantial influences on how the lines between the dots are expressed. The "living moment" also has its impact, allowing us to imbue the more quirky, mercurial nature of flesh and gesture to add depth and nuance to our sculpture.

In the next part then, we’ll finish up with the last third of the muscle inventory, so until then…keep stretching ahead with your creative sensibilities!

“What we have to do is to be forever curiously testing new opinions and courting new impressions.” ~ Walter Pater

Heads Above The Rest!; Exploring The Science and Art Of The Equine Head for Sculpting: Part 9

Introduction

Hey there! Welcome back to this 20–part series examining the equine head, anatomically, biologically, and artistically. So far we’ve covered a lot of ground, but we’ve got many more features to explore. But now that we've laid down a bit of a foundation, we can progress to muscles and other fleshy bits that are so important for our clay, too. Yet we shouldn't let the seeming simplicity of the equine head musculature fool us. It's really quite complicated even though it’s relatively sparse only because so much of it is interlaced, making many deep layers and superficial layers rather arbitrary distinctions. It's also capable of so much motion and expression, of even the subtlest of tweaks, that it can be a real challenge to portray well. There's also a lot to juggle and balance because so much is crammed into such a relatively small space. 

For these reasons then, the muscles are separated into multiple parts to keep posts to a manageable, chewable size. So without further adieu, let’s just get to it, shall we?…

 Muscles

Much of the skull is close to the surface while most of the cartilage is subcutaneous despite it all being interlaced with a network of delicate muscles, fascia, tendons, ligaments, and hide. Muscles on the head tend to be flat or strap–like, too, with fleshy muscle bellies reserved mostly for specific muscles such as the Buccinator and Masseter, on the sides of the head. Overall, the flesh of the head can be categorized into nine basic types, as follows:

• Orbital
• Eyelids
• Ear
• Upper face and mandible
• Muzzle and mid–face
• Nostrils
• Tongue
• Hyoid Apparatus
• Cutaneous muscles

Orbital Muscles

There are seven basic muscles of the orb—four straight muscles, two oblique muscles, and one retractor muscle. They’re small and encased in fascia connecting them to each other and to the lids. There also exist three muscles within the orb itself, which are tiny. That said, however, the movements of the orb within the socket aren’t as straight–forward as implied by these muscle attachments because, together, they produce rather complex movements. Also, the insertions of the rectus muscles aren’t at equal distances from the orb’s equator and the actions of the oblique muscles aren’t consistent with the longitudinal axis of the orb. In short, it’s not as simple as it seems! Nevertheless, the orbital muscles are, as follows:

• Obliquus dorsalis superior (also called the dorsal oblique): The narrowest and longest of the eye muscles, it makes a 90˚ turn at the trochlea attached to the front part of the orbit’s medial wall, the medial border of the optic foramen (which has a bursa at that point) to then continue to its insertion, dorsal on the orb, deep to the insertion of the rectus dorsalis. It rotates the orb on an inward axis, raising the front of the pupil in a spinning motion. It gets its blood supply from the external ophthalmic artery and its nerve supply from the trochlear nerve.
• Obliquus ventralis inferior (also called the ventral oblique): A wide, short muscle, it arises ventral to the fossa of the lacrimal sac to curve around the rectus ventralis then towards its insertion,  ventrolaterrally on the orb passing superficially to the rectus ventralis and partly beneath the rectus lateralis. It rotates the orb on an outward axis, lowering the front of the pupil in a spinning motion. Its blood supply is the external ophthalmic artery and its nerve supply is the oculomotor nerve.
• Rectus dorsalis (also called dorsal rectus): A band–like muscle that inserts by thin tendons just in front of the equator of the orb. It originates on the sphenoid bone next to the optic foramen via a common tendinous ring on the pterygoid crest and around the optic foramen with the rectus lateralis, rectus ventralis, and the rectus medialis to then insert on the dorsal surface of orb. It rotates the pupil rostral and up (upwards, on a horizontal axis). When all rectus muscles are contracting, they can retract the orb into the orbit. Blood is supplied by the external ophthalmic artery and nerve impulses by the oculomotor nerve.
• Rectus ventralis (also called ventral rectus): A band–like muscle that inserts by thin tendons just in front of the equator of the orb. Originating on the sphenoid bone next to the optic foramen via a common tendinous ring on the pterygoid crest and around the optic foramen with the rectus dorsalis, rectus lateralis, and rectus medialis, it inserts on the ventral surface of orb. It rotates the orb rostral and down (downwards, on a horizontal axis), and when all rectus muscles are contracting, they can retract the orb into the orbit. The external ophthalmic artery supplies blood and the oculomotor nerve provides nerve impulses.
• Rectus lateralis (also called lateral rectus): A band-like muscle that inserts by thin tendons just in front of the equator of the orb. This muscle originates on the sphenoid bone next to the optic foramen via a common tendinous ring on the pterygoid crest and around the optic foramen with the rectus lateralis, rectus ventralis, and the rectus medialis. It then inserts on the lateral rostral surface of orb. It rotates the pupil forwards (laterally, on a perpendicular axis). The external ophthalmic artery provides blood and the abducent nerve is the source of impulses.
• Rectus medialis (also called medial rectus): A band–like muscle that inserts by thin tendons just in front of the equator of the orb. Its origin is the sphenoid bone next to the optic foramen via a common tendinous ring on the pterygoid crest and around the optic foramen with the rectus dorsalis, rectus lateralis, and the rectus ventralis. It inserts on the medial surface of orb. It rotates orb rostral medially (backwards on a perpendicular axis). The external ophthalmic artery is its blood supply and its innervated by the oculomotor nerve.
• Retractor bulbi (also called the retractor oculi): It encloses the optic nerve and originates between the optic foramen and the orbital fissure and inserts on the orb, caudal to equator. It retracts orb into the orbit. The facial and palato-labial arteries supply blood and the oculomotor nerve and lateral portion of the abducent nerve supply nerve impulses.
• Cillary muscle (also called the ciliaris): A smooth muscle with circular fibers that suspend the lens within the orb. Its contraction or relaxation focuses the lens. However, it’s thought that the cillary muscles of the horse are poorly developed, having a limited ability to change the shape of the lens to view nearby objects well. Its origin is the scleral ring and it inserts on the lens capsule by tiny fibers. It works to reshape the lens for focusing. The facial and palato–labial arteries supply blood and the parasympthatic fibers from the short ciliary nerve provide impulses.
• Sphincter pupillæ: This is a smooth muscle within the iris, surrounding the pupil, mostly with concentric fibers. It originates as a circular course around the border of the pupil and acts to constrict the pupil. Blood is supplied by the facial and palato-labial arteries, and nerve impulses by the parasympathetic fibers from the oculomotor nerve.
• Dilator pupillæ: A smooth muscle within the iris with fibers that radiate outward. Its origin is a radial course around the border of the pupil and its action dilates pupil. Its blood supply is the facial and palato-labial arteries and its nerve impulses are supplied by its sympathetic fibers.

Muscles Of The Eye Lids

The eyelids are thin and delicate, and highly expressive. They can be pigmented (various shades of black, charcoal, brown, or even a pinkish, purply, or blueish brown or mocha), partially pigmented (“mottled”), or unpigmented (pink), depending on coat color or pattern. They’re divided into four basic layers—the skin, the eyelid muscles, the fibrous tarsal plate, and the innermost palpebral conjunctival layer. For simplicity, however, we’ll only deal with the muscles and the skin:

• Levator palpebræ superioris: A thin band of muscle about half an inch wide that runs above the rectus dorsalis, laying almost entirely within the orbit. It originates dorsal to the optic foramen along the pterygoid crest; it’s more narrow at its origin, and inserts on the upper eyelid by a thin, broad tendon. It raises the upper eyelid. It gets its blood supply from the Ophthalmic artery, and nerve supply from the Oculomotor nerve.
• Orbicularis palpebrarum (also called the Orbicularis oculi): A flat, elliptical sphincter muscle encircling the orbit and partially onto the orb. It’s upper portion is broader and better developed than the lower portion, and forms the shapes of the lids. Its primary attachment to the skull is through the skin of the lids and to the lacrimal bone and tubercle to insert on the eye lids, serving to open and close the eye. Blood is supplied by the facial, transverse, facial, supraorbital and infraorbital arteries. It gets its nerve impulses from the facial nerve.
• Corrugator supercilii (also called the levator anguli oculi medialis, or the levator muscle of the eye): A small, thin, triangular muscle. It originates on the frontal bone, and inserts by blending with the Obricularis palpebrarum in the upper anterior corner of the eye. It works to pull the Orbicularis palpebrarum upward, wrinkling the skin above the eye, but not affecting the shape of the upper lid itself. Blood is supplied by the facial, transverse, facial, supraorbital and infraorbital arteries and nerve impulses from the facial nerve
• Malaris (also called the lachrymal, or the depressor muscle of the eye): A flat muscle that originates on the masseteric ridge and inserts by blending with the Obicularis palpebrarum. It works to pull down the lower eyelid, enlarging the eye by rounding the lower rim. This muscle is variable among individuals and may account for some subtle differences in expression between individuals or breeds. Blood is supplied by the facial, transverse, facial, supraorbital and infraorbital arteries, and nerve impulses come from the facial nerve.

Muscles Of The Ear

Finding reliable anatomical references for the equine ear muscles is surprisingly difficult, largely being treated lightly or even outright ignored. They’re also often referenced differently and muscles may be included with others, creating rather confusing interpretations. The best reference, however, can be found in the book, ANATOMY OF THE DOMESTIC ANIMALS by Sisson and Grossman, 4th Edition. That in mind, ear muscles can be described, as follows:

• Scutularis: A thin sheet of subcutaneous membranous muscle overlaying the Temporalis muscle. It originates on the zygomatic arch and the frontal and parietal crests to insert on the scutiform cartilage. It can be described in three parts (sometimes it’s described as three separate muscles in other references). Yet, in total, this muscle stabilizes the scutiform cartilage and rotates the ear forwards to varying degrees depending on the characteristics of each branch or expression. These three parts are: (1) Frontoscutularis (also written as Fronto-scutularis pars temporalis, or Fronto-scutularis, Attollens anticus, Scutularis, or the Temporoauricularis, with a frontal and temporal portion): Each portion is a flat, band-like muscle. It arises from the zygomatic arch and the frontal crest, and inserts on the lateral (from the zygomatic arch or temporal portion) and anterior borders (from the frontal crest or frontal portion) of the scutiform cartilage, (2) Interscutularis (also called Interscutular muscle, or the Attollens maximus, or simply the Scutularis): A broad, band-like flat muscle that fans slightly forwards down the median. The two bilateral parts of this muscle converge a bit down the median, giving them impression that the muscle goes between both scutiform cartilages. It arises from the parietal crest (the crista sagittalis) and inserts on the medial rim of the scutiform cartilage, (3) Cervicoscutularis (also written Cervico-scutularis): Not clearly defined from the Interscutularis (and often regarded as the same muscle in some references). Like the Interscutularis, it’s also a broad, band-like flat muscle that fans slightly down the median, but backwards. It arises from the nuchal crest and ridge of the occipital bone, and inserts on the medial rim of the scutiform cartilage.
• Zygomaticoauricularis (also written Zygomatico-auricularis, or the External adductor of the auricle): A flat, band-like muscle that originates on the zygomatic arch and the parotid fascia, and inserts on the outer face of the conchal cartilage at its base, but partially under and partially above the insertion of the Parietoauricularis. It pulls the ear forward.
• Scutuloauricularis superficialis inferior (also written Scutulo-auricularis superficialis inferior, or the Inferior adductor of the auricle): A flat, band-like muscle that originates on the lateral aspect of the scutiform cartilage to insert on the base of the conchal cartilage beneath of the insertion of the Zygomaticoauricularis. It pulls the ear forward.
• Scutuloauricularis superficialis medius (also written Scutulo-auricularis superficialis medius or referred to as the Superior adductor of the auricle when interpreted as part of the Scutuloauricularis superficialis superior): A wide, flat band of muscle that originates on the posterior of the deep surface of the scutiform cartilage, and inserts on the dorsal aspect of the conchal cartilage bulb. It receives a slip from the Cervicoscutularis. It pulls the ear forward and erected upright.
• Scutuloauricularis superficialis superior (also written Scutulo-auricularis superficialis superior, the Scutuloauricularis profundi, or the Superior adductor of the auricle when interpreted as part of the Scutuloauricularis superficialis medius): A thin, flat band of muscle that appears as a prolongation of the Interscutularis (and sometimes considered part of that muscle in some references). It arises from the parietal crest (or from the Interscutularis, depending on the reference used) to pass over the medial rim of the scutiform cartilage to insert on the back top portion of the conchal cartilage’s bulb. It pulls the ear forward and erected upright.
• Scutuloauricularis superficialis accessorius (also written Scutulo-auricularis superficialis accessorius): A thin, narrow band of muscle, partially covered by the Scutuloauricularis superficialis superior. It originates on the posterior bulge and surrounding superficial areas of the scutiform cartilage, and inserts on the dorsal convex surface of the conchal cartilage, just behind the scutuloauricularis superficialis superior. It pulls the ear upward and rotates the ear backward.
• Parietoauricularis (also written Parieto-auricularis, or the Levator of the auricle): A flat, triangular muscle arising by a broad fan at the parietal crest under the Cervicoscutularis, passing a little backward and inserting by a narrow band on the lower aspect of the convex surface of the chonchal cartilage bulb, under the Cervicoauricularis superficialis. It rotates the ear backward.
• Cervicoauricularis superficialis (also written as Cervico-auricularis superficialis): A thin, triangular muscle that originates by a broad fan at the nuchal crest and the neighboring aspect of the nuchal ligament, becoming narrower as to runs to its insertion on the medial aspect of the convex surface of the conchal cartilage. It pulls the ear upright and rotated backwards.
• Cervicoauricularis profundus major (also called the Cervicoauricular muscle, the Caudal auricular, or as the Cervico-auricularis profundus major): A thin sheet of muscle that originates on the nuchal ligament, partially under and behind the Cervicoauricularis superficialis. It inserts on the posterior side aspect of the conchal cartilage bulb, partially under the Parotidoauricularis. It pulls the ear backward and rotated backwards.
• Cervicoauricularis profundus minor: A thin sheet of muscle that originates under the Cervicoauricularis profundus major, passing downward to insert on the lowest aspect of the conchal cartilage “bulb,” partially under the parotid gland. It pulls the ear downward and rotated backwards.
• Parotidoauricularis (also written Parotido-auricularis, the Depressor of the auricle, the Ventral auricular, or the Parotidoauricular muscle): A broad, band-like thin muscle that lays over the parotid gland behind the ramus, becoming a bit thicker and more narrow as it runs to the ear. It originates on the fascia of the parotid gland and inserts on the conchal cartilage, just below the “V” made by the two rims. It pulls the ear laterally and downwards.
• Scutuloauricularis profundus major (also written Scutulo-auricularis profundus major, the Abductor of the auricle, or the Scuto-auricularis externus): A flat, thin muscle about one inch wide that arises on the deep surface of the scutiform cartilage and inserts on the most prominent aspect of the conchal cartilage bulb. It pulls and rotates the ear forward.
• Scutuloauricularis profundus minor (also written Scutulo-auricularis profundus minor): A flat, thin muscle about one inch long that originates on the posterior aspect of the deep surface of the scutiform cartilage and the Cervicoscutularis, passing backwards and downwards. It inserts on the base of the concha cartilage, under the Scutuloauricularis profundus major. It pulls and rotates the ear forward.
• Tragicus (also called the Mastoido-auricularis): A small, thin, basilar muscle embedded in the fat that pads the conchal cartilage in the skull. It arises on the temporal bone behind the external acoustic process (or external auditory meatus) and over the annular cartilage, passing upwards to its insertion. It inserts on the lower aspect of the anterior surface of the conchal cartilage. It pulls the conchal cartilage towards the external auditory meatus.
• Antitragicus: A tiny, thin muscle comprised of just a few muscle bundles, partially blended with the Parotidoauricularis. It arises from the bulb of the conchal cartilage behind the “V,” and inserts, flowing into the depression made by the “V,” to blend with the Parotidoauricularis. It has no discernible action by itself.
• Helicis: A tiny, thin muscle that arises from the anterior rim of the conchal cartilage, and inserts, flowing into the depression made by the “V,” to blend with the Parotidoauricularis. It has no discernible action by itself.
• Verticalis auriculæ: A thin sheet of muscular and tendinous fibers that arises from the bulb of the conchal cartilage to insert on the convex dorsal surface of the conchal cartilage. It has no discernible action by itself.
• Styloauricularis: (?) Helps to pull down the ear. Unclear presence in multiple references.

Conclusion To Part 9

That’s a lot to mull over, isn’t it? Oh, but wait—there’s more! You’re not gettin' off that easy! In many ways, the head is perhaps the most difficult part of the equine's anatomy to truly understand and portray. There's just so much, in such a comparatively small area. Because the head has to do so much with so little, too, everything seems to serve multiple purposes which only adds to the complexity of their structure and relationships. To truly understand his head also means we come to truly understand what it means to be equine as well, something that informs the rest of what we do. The head has much to teach us, and if we remain open, we'll absorb all the lessons it offers. 

Approaching the head with some measure of humility is a good idea, too. It's a magnificent and utterly unique example of organic engineering, and we should respect its Biologic. It has purpose, it has consequences, and it has context—it's not just something we like to look at. In Part 10 then we’ll continue with facial muscling, so until next time…just muscle through it!

“My work is not repetition. It is an exploration.” ~ Guido Molinari