THE POSTERIOR AURICULAR ARTERY 543 



upward and backward to the interval between the mastoid process of the temporal 

 bone and transverse process of the atlas, and, after running horizontally backward 

 in a groove on the mastoid portion of the temporal bone, again turns upward, and 

 ends by ramifying in the scalp over the back of the skull, extending as far forward 

 as the vertex. 



The vessel may be divided into three parts — viz., that anterior to the sterno- 

 mastoid miiscle; that beneath the sterno-mastoid; and that posterior to the 

 sterno-mastoid. 



In the first part of its course the occipital artery is covered by the integuments and fascia, 

 and is more or less overlapped by the posterior belly of the digastric muscle, the parotid gland, 

 and posterior facial (temporo-maxillary) vein. It is crossed by the hypoglossal nerve as the 

 latter winds forward over the carotid vessels to reach the tongue. It successively crosses in 

 front of the internal carotid artery, the hypoglossal nerve, the vagus nerve, the internal jugular 

 vein, and the spinal accessory nerve. 



In the second part of its course it sinks deeply beneath the digastric muscle into the interval 

 between the mastoid process of the temporal bone and the transverse process of the atlas. It 

 is here covered by the sterno-mastoid, splenius capitis, and longissimus capitis muscles and by 

 the origin of the digastric; and lies, first on the rectus capitis lateralis, which separates it from 

 the vertebral ai-tery, then in a groove, the occipital groove, on the mastoid portion of the tem- 

 poral bone, and then on the insertion of the superior oblique muscle. 



In the third part of its course it enters the triangular interval formed by the diverging borders 

 of the splenius capitis and the superior nuchal line of the occipital bone. Here it lies beneath 

 the integunients and the aponeurosis uniting the occipital attachments of the sterno-mastoid 

 and trapezius, and rests upon the semi-spinalis capitis (complexus) just before the insertion of 

 that muscle into the occipital bone. In company with the greater occipital nerve, it perforates 

 either this aponeurosis, or less often the posterior belly of the epicranius (occipito-frontalis), 

 and follows roughly, but in a tortuous course, the hne of the lamboid suture, lying between the 

 integument and the cranial aponeurosis. In the scalp it divides into several large branches, 

 which ramify over the back of the skull and reach as far forward as the vertex. They anasto- 

 mose with the corresponding branches of the opposite side, and with the posterior auricular 

 and the superficial temporal arteries. 



Branches of the Occipital Artery (Fig. 450) 



The branches of the occipital artery are: — (1) The muscular; (2) the menin- 

 geal; (3) the auricular; (4) the mastoid; (5) the descending; (6) the occipital. 



(1) The muscular branches [rami musculares] (fig. 450) supply the sternocleidomastoid and 

 adjacent muscles. One of these branches may take the place of the sterno-mastoid branch of 

 the external carotid. The hypoglossal nerve then, as a rule, loops round it instead of round the 

 occipital. 



(2) The meningeal branches [rami meningei] (fig. 450), one or more in number, are long 

 slender vessels which leave the occipital artery as it crosses the internal jugular vein and, ascend- 

 ing along the vessel, pass with it through the jugular or hypoglossal foramen, and are distributed 

 to the dura mater lining the posterior fossa of the skull. 



(3) The auricular branch [ramus auricularis] ascends over the mastoid process to the back 

 of the ear, and supplies the pinna and concha. It sometimes takes the place of the posterior 

 auricular artery (fig. 450). 



(4) The mastoid branch [ramus mastoideus] is a small twig that passes into the skull through 

 the mastoid foramen, supplying the dura mater, the diploe, the walls of the transverse sinus, 

 and the mastoid ceUs. 



(5) The descending or princeps cervicis [ramus descendens] (fig. 450), the largest of the 

 branches of the occipital, arises from that artery just before it emerges from beneath the splenius, 

 and, descending for a short distance between the splenius and semi-spinalis capitis (complexus), 

 divides into a superficial and a deep branch. The superficial branch perforates the splenius, 

 supplies branches to the trapezius, and anastomoses with the ascending branch of the transverse 

 cervical artery. The deep branch passes downward between the semi-spinalis capitis (com- 

 plexus) and colli, and anastomoses with the deep cervical branch of the costo-cervical trunk 

 and with branches of the vertebral. The anastomoses between the above-mentioned arteries 

 form important collateral channels after Ligature of the common carotid and subclavian arteries 

 (fig. 444). 



(6) The occipital or terminal branches [rami occipitales] (fig. 450), usually two in number, 

 named from their position medial and lateral, ramify over the scalp, and have already been 

 described. The medial branch generally gives off a twig which enters the parietal foramen 

 (parietal artery) and is distributed to the dura mater. The occipital artery may also give off 

 the stylo-mastoid, the posterior auricular, or the ascending pharyngeal arteries. 



7. THE POSTERIOR AURICULAR ARTERY 



The posterior auricular artery [a. auricularis posterior] (fig. 450) arises from 

 the posterior part of the external carotid artery, usually immediately above the 



