BEANCHES OF THE EXTERNAL CAKOTID AETEEY. 895 



: elly of the digastric, and the anterior part of the sterno-mastoid muscle, and, close to its 

 -, rigin, it is crossed by the hypoglossal nerve. In the second and more horizontal part of 

 ,3 course, it is still under cover of the sterno-mastoid and digastric, and lies, medially, 

 ; gainst the rectus capitis lateralis, which separates it from the vertebral artery. In the 

 'iird part of its course it rests upon the superior oblique and semispinalis capitis (O.T. 

 mplexus), under cover of the sterno-mastoid, the splenius capitis, and the longis- 

 .mus capitis muscles. Near its termination it is crossed by the great occipital nerve, and 

 , passes either through the trapezius or between the trapezius and the sterno-mastoid, 

 nd pierces the deep fascia of the neck before it enters the superficial fascia of the scalp. 



Branches. (a) Muscular branches go to the surrounding muscles. The sterno- 

 lastoid branch is the most important of this group ; it springs from the commencement 

 f the occipital, is looped downwards across the hypoglossal nerve, and is continued down- 

 ards and posteriorly, below and anterior to the accessory nerve, into the sterno-mastoid 

 mscle, where it anastomoses with the sterno-mastoid branch of the superior thyreoid artery. 

 b is sometimes represented by two or more small branches. 



(6) The meningeal are irregular branches given off from the occipital, anterior to the 

 mstoid process. They enter the posterior fossa of the skull through the hypoglossal 

 anal, or through the jugular foramen; they supply the upper part of the internal 

 agular vein, the sigmoid part of the transverse sinus, and the dura mater in the posterior 

 )ssa of the skull, and they anastomose with the middle meningeal and with meningeal 

 ranches of the ascending pharyngeal artery. 



(c) The mastoid, a small and inconstant branch which arises posterior to the mastoid 

 rocess. It enters the posterior fossa of the skull through the mastoid foramen, supplies 

 lie dura mater, and anastomoses with branches of the middle meningeal artery. 



(d) The descending branch (O.T. princeps cervicis) is given off from the occipital 

 pon the surface of the superior oblique. It passes medially, and at the lateral 



order of the semispinalis capitis it divides into superficial and deep branches. The 

 uperfieial , branch runs over the semispinalis capitis, between it and the trapezius, 

 nd anastomoses with the superficial cervical artery. The deep branch passes between the 

 emispinalis capitis and the underlying semispinalis cervicis, and anastomoses with branches 



' f the vertebral and profunda cervicis arteries. 



(e) The auricular is an inconstant branch which, as a rule, is only given off from 

 he occipital when the posterior auricular artery is absent. It ramifies over the mastoid 

 art of the temporal bone, and supplies the medial surface of the auricle. 



(/) The terminal branches (rami occipitales) are medial and lateral. They ramify 

 i the superficial fascia of the posterior part of the scalp, where they anastomose with the 

 ; osterior auricular and superficial temporal arteries. Both branches are accompanied by 

 ranches of the great occipital nerve. The medial branch gives off a meningeal twig, 

 T hich passes into the skull through the parietal foramen, to supply the walls of the 

 uperior sagittal sinus and to anastomose with the middle meningeal artery. 



(5) Arteria Auricularis Posterior. The posterior auricular artery (Figs. 759, 

 60, 787) springs from the posterior aspect of the external carotid immediately 



1 bove the posterior belly of the digastric muscle, and it terminates between the 

 aastoid process and the back of the auricle by dividing into mastoid and auricular 

 ranches. 



Course and Relations. Commencing at the upper border of the posterior 

 elly of the digastric, it runs upwards and posteriorly, under cover of the postero- 

 aedial surface of the parotid gland, to the interval between the mastoid process 

 ud the external acoustic meatus. It is accompanied in the terminal part of its 



1 ourse by the posterior auricular branch of the facial nerve. 



Branches. (a) Muscular branches are given to the sterno-mastoid, the digastric, 

 nd the styloid group of muscles. 



(b) Parotid branches pass to the lower and posterior part of the parotid gland. 



(c) A stylo-mastoid branch is given off at the lower border of the external acoustic 

 neatus. It runs upwards, by the side of the facial nerve, enters the stylo-mastoid foramen, 

 -nd ascends, in the canalis facialis (Fallopius), to the upper part of the medial wall of the 

 ympanum, where it terminates by anastomosing with the petrosal branch of the middle 

 neningeal artery. It supplies branches to the external acoustic meatus, the mastoid cells, 



3 vestibule, and semicircular canals, the stapedius muscle, and a posterior tympanic 

 'ranch which anastomoses with the anterior tympanic branch of the internal maxillary, 

 Mining, in young subjects, a vascular circle around the membrana tympani ; other branches 



