THE EXTERNAL CAROTID ARTERY 557 



and supplies the dura mater, the diploe, and the mastoid cells; this latter branch 

 sometimes arises from the occipital artery, and is then known as the mastoid branch. 



The Meningeal Branch (ramus meningeus; dural branch} ascends with the internal 

 jugular vein, and enters the skull through the jugular foramen and condyloid 

 canal, to supply the dura mater in the posterior fossa. 



The Descending Branch (ramus descendens; arteria princeps cenicis) (Fig. 513), 

 the largest branch of the occipital, descends on the back of the neck, and divides 

 into a superficial and deep portion. The superficial portion runs beneath the 

 Splenius, giving off branches which pierce that muscle to supply the Trapezius and 

 anastomose with the ascending branch of the transverse cervical : the deep portion 

 runs down between the Semispinales capitis and colli, and anastomoses w r ith the 

 vertebral and with the a. profunda cervicalis, a branch of the costocervical trunk. 

 The anastomosis between these vessels assists in establishing the collateral circu- 

 lation after ligature of the common carotid or subclavian artery. 



The terminal branches of the occipital artery are distributed to the back of the 

 head: they are very tortuous, and lie between the integument and Occipitalis, 

 anastomosing with the artery of the opposite side and with the posterior auricular 

 and temporal arteries, and supplying the Occipitalis, the integument, and peri- 

 cranium. One of the terminal branches may give off a meningeal tw 7 ig which passes 

 through the parietal foramen. 



5. The posterior auricular artery (a. auricularis posterior) (Fig. 508) is small 

 and arises from the external carotid, above the Digastricus and Stylohyoideus, 

 opposite the apex of the styloid process. It ascends, under cover of the parotid 

 gland, on the styloid process of the temporal bone, to the groove between the 

 cartilage of the ear and the mastoid process, immediately above which it divides 

 into its auricular and occipital branches. 



Branches. Besides several small branches to the Digastricus, Stylohyoideus, 

 and Sternocleidomastoideus, and to the parotid gland, this vessel gives off three 

 branches : 





Stylomastoid. Auricular. Occipital. 



The Stylomastoid Artery (a. stylomastoidea) enters the stylomastoid foramen and 

 supplies the tympanic cavity, the tympanic antrum and mastoid cells, and the 

 semicircular canals. In the young subject a branch from this vessel forms, with 

 the anterior tympanic artery from the internal maxillary, a vascular circle, which 

 surrounds the tympanic membrane, and from which delicate vessels ramify on that 

 membrane. It anastomoses with the superficial petrosal branch of the middle 

 meningeal artery fry a twig which enters the hiatus canalis facialis. 



The Auricular Branch (ramus auricularis} ascends behind the ear, beneath the 

 Auricularis posterior, and is distributed to the back of the auricula, upon which 

 it ramifies minutely, some branches 'curving around the margin of the cartilage, 

 others perforating it, to supply the anterior surface. It anastomoses with the 

 parietal and anterior auricular branches of the superficial temporal. 



The Occipital Branch (ramus Occipitalis') passes backward, over the Sternocleido- 

 mastoideus, to the scalp above and behind the ear. It supplies the Occipitalis 

 and the scalp in this situation and anastomoses with the occipital artery. 



6. The ascending pharyngeal artery (a. pharyngea ascendens) (Fig. 513), the 

 smallest branch of the external carotid, is a long, slender vessel, deeply seated in 

 the neck, beneath the other branches of the external carotid and under the Stylo- 

 pharyngeus. It arises from the back part of the external carotid, near the com- 

 mencement of that vessel, and ascends vertically between the internal carotid 

 and the side of the pharynx, to the under surface of the base of the skull, lying 

 on the Longus capitis. 





