64 TOPOGRAPHIC AND APPLIED ANATOMY. 



FIG. 24. The anterior cervical region (the hypoglossal nerve has been displaced slightly downward). 



the common carotid artery is situated the internal jugular vein, which when well filled \vith blood 

 partly overlies the carotid, so that the artery is more deeply placed than the vein. Behind and 

 between these two vessels, and enclosed within their common connective-tissue sheath, the vagus 

 nerve (see Figs. 25 and 27 and Plate 5) runs downward to the upper opening of the thorax. When 

 the great vessels of the neck are injured, this nerve is also easily involved; it should be carefully 

 avoided in ligation of the carotid. The good operator should also spare the descendens hypoglossi 

 nerve (see Figs. 24 and 25), which runs downward upon the carotid sheath, although its division is 

 not followed by important symptoms. This small nerve, together with branches from the second 

 and third cervical nerves, forms the ansa hypoglossi, from which the infrahyoid muscles receive 

 their motor branches. One or two superior thyroid veins may run almost transversely across the 

 carotid (see Fig. 27) and also aid in rendering the ligation of the vessel more difficult. At the 

 margin of the omohyoid muscle may be seen the thyroid gland, which projects into the carotid 

 triangle to a varying extent, dependent upon the degree of its development. The superior thyroid 

 artery, the first branch of the external carotid, runs downward to this gland in an arched and 

 tortuous direction. It gives off the small superior laryngeal artery, which, together with the 

 sensory superior laryngeal nerve from the pneumogastric, enters the larynx through the thyro- 

 hyoid membrane below the greater cornu of the hyoid bone. The lingual artery is given off 

 from the external carotid above the superior thyroid; it runs anteriorly and soon disappears 

 beneath the hyoglossus muscle to supply the tongue. It must sometimes be ligated to control 

 hemorrhage after injuries to the tongue or for the purpose of preventing hemorrhage during opera- 

 tions for lingual carcinoma. The vessel may be easily exposed by an incision just above the 

 greater cornu of the hyoid bone; after dividing the skin, the platysma, the deep fascia, and the 

 hyoglossus muscle, the artery will be found in the angle between the posterior belly of the digastric 

 muscle and the greater cornu of the hyoid bone. The artery may also be ligated further anteriorly 

 in the submaxillary triangle. Just above the lingual artery (and often arising with it from a 

 common trunk) is given off the third of the three anterior branches of the external carotid the 

 facial artery. This is the largest vessel in the submaxillary triangle (see page 65), and it enters 

 this region by passing beneath the posterior belly of the digastric and the 'stylohyoid muscles. 

 The other branches of the external carotid in the carotid triangle are the ascending pharyngeal 

 artery, passing upward and inward to the base of the skull, and the occipital artery, which runs 

 upward and backward (see Plate 2). The carotid artery is accompanied by a chain of deep 

 cervical lymphatic glands which frequently become diseased. Abscesses originating within these 

 glands may point along the vessels until they reach the connective tissue of the mediastinum, from 

 which situation the pus may extend in various directions. 



The hypoglossal nerve, the motor nerve of the tongue, is found in the upper portion of the 

 carotid triangle ; it passes forward in a curved direction, the convexity being downward, crosses 

 the external carotid and then the facial artery, and enters the submaxillary region in company with 

 the lingual vein by passing underneath the posterior belly of the digastric muscle. The esophagus 

 and the lower portion of the pharynx may be reached through the carotid triangle by an incision 

 made along the inner margin of the sternocleidomastoid muscle (see page 67). 



