494 THE BLOOD-VASCULAR SYSTEM. 



portion. The former runs beneath the Splenius, giving off' branches which per- 

 forate that muscle to supply the Trapezius, which anastomose with the superficial 

 cervical artery, a branch of the transversalis colli : the latter passes beneath the 

 Complexus between it and the Semispinalis colli, and anastomoses with branches 

 from the vertebral and with the deep cervical artery, a branch of the superior 

 intercostal. The anastomosis between these vessels serves mainly to establish the 

 collateral circulation after ligation of the carotid or subclavian artery. 



The cranial branches of the occipital artery are distributed upon the occiput ; 

 they are very tortuous, and lie between the integument and Occipito-frontalis, 

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

 temporal arteries. They supply the back part of the Occipito-frontalis muscle, 

 the integument, and pericranium. 



The Posterior Auricular Artery (Fig. 285) is a small vessel which arises from 

 the external carotid, above the Digastric and Stylo-hyoid muscles, 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 two terminal 

 branches, the auricular and mastoid. Just before arriving at the mastoid process, 

 this artery is crossed by the portio dura, and has beneath it the spinal accessory 

 nerve. 



Besides several small branches to the Digastric, Stylo-hyoid, and Sterno-mas- 

 toid muscles and to the parotid gland, this vessel gives off three branches : 



Stylo-mastoid. Auricular. Mastoid. 



The stylo-mastoid branch enters the stylo-mastoid foramen, and supplies the 

 tympanum, mastoid cells, and semicircular canals. In the young subject a branch 

 from this vessel forms, with the tympanic branch from the internal maxillary, a 

 vascular circle, which surrounds the membrana tympani, and from which delicate 

 vessels ramify on that membrane. It anastomoses with the petrosal branch of the 

 middle meningeal artery by a twig which enters the hiatus Fallopii. 



The auricular branch, one of the terminal branches, ascends behind the ear, 

 beneath the Retrahens auriculam muscle, and is distributed to the back part of 

 the cartilage of the ear, upon Avhich it ramifies minutely, some branches curving 

 round the margin of the fibro- cartilage, others perforating it, to supply its anterior 

 surface. It anastomoses with the posterior branch of the superficial temporal and 

 also with its anterior auricular branches. 



The mastoid branch passes backward, over the Sterno-mastoid muscle, to the 

 scalp above and behind the ear. It supplies the posterior belly of the Occipito-fron- 

 talis muscle and the scalp in this situation. It anastomoses with the occipital artery. 



The Ascending Pharyngeal Artery (Fig. 289), 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 the Stylo-pharyngeus muscle. It arises 

 from the back part of the external carotid, near the commencement 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 Rectus capitis anticus major. 

 Its branches may be subdivided into four sets : 



Prevertebral. Pharyngeal. Tympanic. Meningeal. 



The prevertebral branches are numerous small vessels which supply the Recti 

 capitis antici and Longus colli muscles, the sympathetic, hypoglossal, and pneu- 

 mogastric nerves, and the lymphatic glands, anastomosing with the ascending 

 cervical artery. 



The pharyngeal branches are three or four in number. Two of these descend 

 to supply the middle and inferior Constrictors and the Stylo-pharyngeus, ramifying 

 in their substance and in the mucous membrane lining them. The largest of the 

 pharyngeal branches passes inward, running upon the Superior constrictor, and 

 sends ramifications to the soft palate and tonsil, which take the place of the 



