220 



FASCIA AND MUSCLES OF THE HORSE 



Origin. — The crest formed by the pterygoid process of the sphenoid and the 

 palate bone. 



Insertion. — The concave inner surface of the broad portion of the ramus of the 

 mandible, and the inner lip of the lower border. 



Action. — Acting together, to raise the lower jaw; acting singly, to produce also 

 lateral movement of the jaw. 



Structure. — The muscle is capable of division into two parts. The principal 

 part is superficial (internal), and its fibers are, for the most part, vertical in direc- 

 tion. It contains much tendinous tissue (septa). The smaller portion is external 

 to the foregoing, and its fibers are directed downward and Ijackward. 



Relations. — Externally, the ramus of the mandible, the external pterygoid 

 muscle, the inferior alveolar vessels and nerve, and the lingual and mylo-hyoid 

 nerves; internally, the great cornu of the hyoid bone, the tensor palati, pterygo- 



Ethmo- 



turbinals 



Superior meatus 



Superior turbinat 



Middle viealuk 



Inferior turbinat 



Inferior meatus 



Septum of 

 frontal sinuses 



Stylo- 

 7nn.vil- 

 laris 



Diyastricus, 

 jMstcriar 

 belly 



Digastricus, 

 anterior belly 



Intermediate tendon 



Fig. 175. — Sagittal Section op Head of Horse, Showing Deep Pterygo-maxillary Region, and Nasal. 



AND Cranial Cavities. 

 /, Cerebral compartment of cranial cavity; 2, cerebellar compartment of same; 3, tentorium osseum; 

 /,, tentorium cerebelli; 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. 



pharyngeus, palato-pharyngeus, mylo-hyoideus, digastricus, and stylo-hyoideus 

 muscles, the guttural pouch, the external maxillary vessels, the ninth and twelfth 

 nerves, the submaxillary salivary gland, the submaxillary and parotid ducts, and 

 the submaxillary and pharyngeal lymph-glands. 



Blood-supply. — Internal maxillary, masseteric, and inferior alveolar arteries. 



Nerve-supply. — Mandibular nerve. 



4. Pterygoideus externus (s. lateralis) .—This muscle is considerably smaller 

 than the preceding one, and is situated external to its upper part. 



Origin. — The external surface of the pterygoid process of the sphenoid 

 bone. 



Insertion. — The inner surface of the neck and the inner part of the anterior 

 border of the condyle of the mandible. 



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

 move the jaw laterally, i. e., toward the side opposite to the muscle acting. The 



