262 FASCLE AND MUSCLES OF THE HORSE 
medially, the great cornu of the hyoid bone, the pharynx, the larynx, the tensor 
palati, mylo-hyoideus, digastricus, and stylo-hyoideus muscles, the guttural pouch, 
the external maxillary vessels, the ninth and twelfth nerves, the mandibular salivary 
gland, the mandibular and parotid ducts, and the mandibular and pharyngeal lymph- 
elands. 
Blood-supply.—Internal maxillary, masseteric, and inferior alveolar arteries. 
Nerve-supply.—Mandibular nerve. 
4. Pterygoideus lateralis (s. externus).—This muscle is considerably smaller 
than the preceding one, and is situated lateral to its upper part. 
Origin.—The lateral surface of the pterygoid process of the sphenoid bone. 
Insertion—The medial surface of the neck, the medial part of the anterior 
border of the condyle of the mandible and the articular disc. 
Action.—Acting together, to draw the lower jaw forward; acting singly, to 
Ethmo- Septum of 
turbinates frontal sinuses 
Dorsal meatus 
Dorsal turbinate 
Middle meatus 
Ventral turbinate 
Ventral meatus 
Occipito- 
mandib- 
ularis 
Digastricus, 
posterior 
belly 
Digastricus, 
anterior belly 
Intermediate tendon 
Fic. 264.—SacitraL Section or Heap or Horse, SHOWING DEEP PTERYGO-MANDIBULAR REGION AND NASAL AND 
CRANIAL CAVITIES. 
1, Cerebral compartment of cranial cavity; 2, cerebellar compartment of same; 3, tentorium osseum; 4, ten- 
torium cerebelli; 45, sphenoidal sinus; 6, hamulus of pterygoid bone-tendon of tensor palati cut off short at anterior 
border of hamulus; 7, mylo-glossus. The olfactory mucous membrane is shaded. 
move the jaw also toward the side opposite to the muscle acting. The latter action 
is due to the fact that the origin is nearer to the median plane than the insertion. 
Structure.-—The muscle is almost entirely fleshy, and the fibers are almost 
longitudinal in direction. Some of them are inserted into the edge of the articular 
disc. 
Relations.—Laterally, the temporo-mandibular articulation and the temporalis 
muscle; medially, the medial pterygoid and tensor palati muscles. The internal 
maxillary artery crosses the ventral face of the muscle and dips in between it and 
the tensor palati. The mandibular nerve lies on the ventral surface, and the bue- 
cinator nerve perforates the origin of the muscle. 
Blood-supply.—Internal maxillary and inferior alveolar arteries. 
Nerve-supply.—Mandibular nerve. 
5. Occipito-mandibularis! (M. jugulomandibularis).—This is a short, fusiform 
1' This muscle is also known as the stylo-maxillaris, stylo-mandibularis, ete. 
