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