262 



FASCIA 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, niasseteric, and inferior alveolar arteries. 



Nerve-supply. — INIandibular 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 condjde of the mandible and the articular disc. 



Action. — Acting together, to draw the lower jaw forward; acting singly, to 



Ethmo- 

 turhinates 

 Dorsal meatus 



Septum of 

 frontal sinuses 



meatus 



^y/o'hyoideuS 

 7 





r 



-Occipito- 

 m.andih- 

 ularis 



^ Digastricus, 

 posterior 

 belly 



Digastricus, 

 anterior helly 



Intermediate tendon 



Fig. 204. — S.^GiTTAL Section of Head of Horse, Showing Deep Pterygo-m-vndibular Region and Nasal and 



Cranial Cavities. 

 1, Cerebral compartment of cranial cavity; 2, cerebellar compartment of same; 5, tentorium osseum; 4. ten- 

 torium cerebeili; 5, 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 mediali plane than the insertion. 



Structure. — The muscle is almost entirely fleshj-,"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 -palatr 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 buc- 

 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, etc. 



