642 BLOOD-VASCULAR SYSTEM OF THE HORSE 



branches also to the medial pterj'goid and occipito-mandibularis muscles and the 

 parotid gland. 



2. The external maxillary artery (A. maxillaris externa)^ arises from the ex- 

 ternal carotid on the deep surface of the posterior belly of the digastricus (Fig. 561). 

 It runs downward and forward on the lateral wall of the pharynx across the deep face 

 of the stylo-hyoideus toward the great cornu of the hyoid bone, accompanied by 

 the glosso-pharyngeal nerve in front and the hypoglossal nerve behind. After 

 giving off the lingual artery at the posterior border of the great cornu, it inclines 

 more ventrally on the medial surface of the medial pterygoid muscle, crosses over 

 the hyo-glossus muscle, the hypoglossal nerve, the mandibular duct, and the inter- 

 mediate tendon of the digastricus, and turns forward in the mandibular space. 

 Here it lies on the lower part of the medial pterygoid muscle, and is related medially 

 to the mandibular lymph glands, above to the anterior belly of the digastricus, and 

 below to the homonymous vein. At the anterior border of the masseter it turns 

 around the ventral border of the jaw and ascends on the face in front of that 

 muscle. At the turn the artery is in front, the vein in the middle, and the parotid 

 duct posterior.^ The artery is conveniently placed at its inflection for taking the 

 pulse, since it is superficial and lies directly on the bone. Beyond this point it is 

 commonly termed the facial artery (A. facialis). The artery and vein pass upward 

 along the anterior border of the masseter, under cover of the facial cutaneus and 

 the zygomaticus, and are crossed superficially by branches of the facial nerve and 

 deeply by the parotid duct. The artery terminates over the levator labii super- 

 ioris proprius by dividing into the dorsal nasal and the angular artery of the ej^e. 

 The chief branches of the external maxillary are as follows : 



(1) The pharyngeal artery (A. palatina ascendens) arises usually behind the 

 stylo-pharyngeus, passes between that muscle and the great cornu, and runs for- 

 ward on the lateral wall of the pharynx under the elastic pharyngeal fascia. It is 

 distributed to the pharynx, soft palate, and tonsil. 



(2) The lingual artery (A. lingualis) is a large branch which diverges from the 

 parent trunk at an acute angle, runs along the ventral border of the great corna 

 of the hyoid bone, and dips under the hyo-glossus muscle. It then passes across 

 the kerato-hyoideus, turns inward under the intercornual joint of the hyoid bone, 

 and runs forward in the tongue between the hyo-glossus and genio-glossus. This 

 part (A. profunda linguae) is flexuous and is accompanied by branches of the hypo- 

 glossal and lingual nerves. It is the chief artery of the tongue, and anastomoses 

 with the opposite artery and the sublingual.^ 



(3) The sublingual artery (A. sublingualis) is a smaller vessel which arises at 

 the anterior extremity of the mandibular gland (Fig. 561). It passes forward on the 

 anterior belly of the digastricus, between the ramus of the mandible and the mylo- 

 hyoideus, perforates the latter, runs along the lower border of the sublingual gland, 

 and ramifies in the mucous membrane of the anterior part of the floor of the mouth. 

 It detaches branches to the muscles and skin in the mandibular space, the mandib- 

 ular lymph glands, and the sublingual gland. It also gives off the small submental 

 artery (A. submentalis), which runs forward superficially toward the lower lip, 

 supplying twigs to the skin and the mylo-hyoideus. 



In some cases the sublingual artery arises from the lingual and the submental from the 

 external maxillary. Sometimes the sublingual remains on the superficial face of the mylo-hyoideus 

 — thus resembUng the submental of man — and the subUngual gland is supphed by a special 

 branch of the lingual. 



' Also termed the submaxillary or facial artery. The term facial may be applied to the artery 

 after it reaches the lateral surface of the face. 



- In exceptional cases the vein is in front of the artery. 



' In some cases the lingual trunk runs on the superficial face of the hypoglossus instead of 

 passing beneath it; in such specimens a small branch extends forward a variable distance under 

 the muscle. 



