OCCIPITAL ARTERY. 425 



tracheal aspect, and are continued to the level of the larynx, 

 where they break up. Throughout their course, they are accom- 

 panied by the par vagum, cervical portion of the sympathetic, 

 and inferiorly by the recurrent nerves, all being enclosed in the 

 same sheath. The arteries are covered at the lower part of the 

 neck by the scalenus and levator humeri ; in the middle by the sub- 

 scapulo-hyoideus, which separates them from the jugular vein; and 

 they are related with the rectus capitus anticus major, and longus 

 colli superiorly. The carotid and jugular are usually separated 

 by slips of the subscapulo-hyoideus, but at the entrance of the 

 thorax they contact, the artery lying superiorly. The carotids 

 give off several small branches to the muscles of the neck, twigs 

 to the trachea and oesophagus, and near their termination, the 

 thyroid and thyro-laryngeal arteries. The thyroid artery enters 

 the inferior part of the thyroid gland, to which it is distributed. 

 The thyro-laryngeal arises just above the latter, opposite the 

 upper tracheal ring, winds round the trachea, and divides into 

 branches, supplying the thyroid body, pharynx, and larynx. 



The carotid artery terminates by a trifurcation, forming the 

 following important arteries : — 



Occipital. I Internal carotid. 



External carotid. 



OCCIPITAL ARTERY. 



(Fig. 163. 1.) 



The occipital artery comes off at the carotid trifurcation. At 

 first it accompanies the internal carotid, then crosses it, and 

 reaches the under surface of the wing of the atlas, at the back of 

 the guttural pouch, passing between the submaxillary gland and 

 anterior straight muscles of the head, through the external anterior 

 foramen of the atlas, and at the upper surface of the latter it 

 divides into the cerehro-spinal and musculo-occipital. It is 

 crossed by the par vagum and spinal accessory nerves and the 

 cervical portion of the sympathetic chain, and accompanied by 

 divisions of the inferior branch of the spinal nerves. Its branches 

 are these : — 



Prevertebral. I Ramus auastomoticus. 



Mastoid. I Musculo-occipital. 



Cerebro-spinal. 



