222 FASCIA AND MUSCLES OF THE HORSE 



maxillary artery crosses the lower face of the muscle and dips in between it and the 

 tensor palati. The mandibular nerve lies on the ventral surface, and the buccinator 

 nerve perforates the origin of the muscle. 



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



Nerve-supply. — Mandibular nerve. 



5. Stylo-maxillaris (s.-mandibularis) (M. jugulomandibularis). — This is a short 

 muscle extending from the paramastoid or styloid process of the occipital bone to 

 the posterior border of the lower jaw; it is covered by the parotid gland. 



Origin. — The paramastoid or styloid process of the occipital bone, in common 

 with the posterior belly of the digastricus. 



Insertion. — The posterior border of the ramus of the mandible. 



Action. — To depress the lower jaw and open the mouth. 



Structure. — The muscle contains a good deal of tendinous tissue. It blends 

 with the posterior belly of the digastricus. 



Relations. — Superficially, the parotid gland, the tendon of the sterno-cephalicus, 

 and the fibrous expansion which connects it with the tendon of the mastoido- 

 humeralis; deeply, the guttural pouch, the external carotid artery, the ninth and 

 twelfth nerves, the pharynx, and the submaxillary gland. 



Blood-supply. — External carotid artery. 



Nerve-supply. — Facial nerve. 



6. Digastricus. — ^This muscle is composed of two fusiform, flattened bellies, 

 united by a round tendon. 



Origin. — The paramastoid or styloid process of the occipital bone, in common 

 with the preceding muscle. 



Insertion. — The inner surface of the lower border of the mandible behind the 

 symphysis. 



Action. — It assists in depressing the lower jaw and opening the mouth. If the 

 mandible be fixed and both bellies contract, the hyoid bone and the base of the 

 tongue are raised, as in the first phase of deglutition. 



Structure. — The posterior belly has the appearance of a branch detached from 

 the inner surface of the stylo-maxillaris. It passes downward and forward, and is 

 succeeded by a small rounded tendon. The latter perforates the tendon of in- 

 sertion of the stylo-hyoideus, and is provided with a synovial sheath. The anterior 

 belly is larger and terminates by thin tendinous bundles. 



Relations. — The posterior belly has practically the same relations as the stylo- 

 maxillaris. The intermediate tendon is in contact externally with the internal 

 pterygoid muscle, the submaxillary gland and duct, and the external maxillary 

 artery. The anterior belly lies in the submaxillary space between the ramus of the 

 jaw and the mylo-hyoideus muscle; the sublingual vessels run along its upper border. 



Blood-supply. — External carotid and sublingual arteries. 



Nerve-supply. — Facial and mandibular nerves. 



THE HYOID MUSCLES 



This group consists of eight muscles, one of which, the hyoideus transversus, 

 is unpaired. 



1. Mylo-hyoideus. — This muscle, together with its fellow, forms a sort of 

 sling between tlie two rami of the lower jaw, in which the tongue is supported. 



Origin. — The inner surface of the alveolar border of the mandilile. 



Insertion. — (1) A median fibrous raphe extending from the symphysis to the 

 hyoid bone; (2) the lingual process and body of the hyoid bone. 



Action. — It raises the floor of the mouth, the tongue, and the hyoid bone. 



Structure. — Each muscle consists of a thin curved sheet, the fibers passing 

 downward from their origin and then curving toward the median raphe. It is 



