132 THE SURGICAL ANATOMY OF THE HORSE 



capitis anticus major muscles. The left common carotid is also 

 related to the oesophagus. The artery is accompanied by the jugular 

 vein, above and slightly internal to which it is placed, but as it passes 

 up the neck the subscapulo-hyoideus muscle passes between the 

 artery and vein. Above the artery and closely related to it is the 

 nerve cord, which is common to the vagus and the cervical portion 

 of" the sympathetic, whilst below the artery is the inferior (recurrent) 

 laryngeal nerve. 



During its course the vessel crosses the trachea obliquely to gain 

 the superior aspect of the cricoid cartilage of the larynx, where it 

 divides into the occipital, external carotid and internal carotid arteries. 

 The common carotid gives off a number of branches to the oesophagus, 

 the trachea, and the muscles which are placed along its course, and 

 towards the upper end of the neck it gives off the thyroid artery, 

 which runs to the thyroid body, the posterior extremity of which it 

 pierces. A little in advance of the origin of the thyroid artery 

 the carotid gives off the thyro-laryngeal artery. This vessel passes 

 to the inner side of the thyroid body, and then splits up into two 

 portions, one of which takes a retrograde direction to enter the 

 anterior face of the body, and the other passes forwards to supply the 

 larynx. 



The Occipital Artery. — This vessel ascends from the cricoid cartilage 

 to the inferior edge of the wing of the atlas. It then passes through the 

 antero-external foramen of the wing, and in the groove connecting the 

 two anterior foramina it splits up into the occipito-muscular and 

 cerebro-spinal arteries. During its course the occipital artery gives 

 off the following collateral branches : 



(i) The pre-vertebrul artery, which is distributed to the muscles 



in front of the vertebrje (longus colli, anterior straight muscles of 



head, etc.). 



(2) The mastoid artery, which passes across the styloid process 



and runs forwards to dip under the edge of the pyramidal process 



