70 DISSECTION OP THE NECK. 



nected with the back of the hyoid bone and the layrnx are some of the 

 constrictor muscles of the gullet. 



Vessels in the triangular space. The carotid bloodvessels, 6 and T , 

 occupy the hinder and deeper part of the space along the side of the 

 sterno-mastoid muscle ; and their course would be marked on the surface 

 by a line from the sterno-clavicular articulation to a point midway between 

 the jaw and the mastoid process. As high as the level of the cricoid car- 

 tilage they are buried beneath the depressor muscles of the os hyoides ; 

 but beyond that spot they are covered by the superficial layers over the 

 space, and by the sterno-mastoid muscle which, before the parts are dis- 

 placed, conceals the vessels as far as the parotid gland. 



For a short distance after its exit from beneath the muscles at the root 

 of the neck, the common carotid artery remains a single trunk, 6 ; but 

 opposite the upper border of the thyroid cartilage it divides into two large 

 vessels, external and internal carotid. From the place of division these 

 trunks are continued onwards, beneath the digastric and stylo-hyoid mus- 

 cles, to the interval between the jaw and the mastoid process. 



At first the trunks lie side by side, the vessel destined for the internal 

 parts of the head (internal carotid) being the more posterior or external 

 of the two; but above the digastric muscle it becomes deeper than the 

 other. The more superficial artery (external carotid) furnishes many 

 branches to the neck and the outer part of the head, vi?., some forwards 

 to the larynx, tongue, and face ; others backwards to the occiput and the 

 ear; and others upwards to the head. 



But the common carotid does not always divide, as here said. For 

 the point of branching of the vessel may be moved from the upper border 

 of the thyroid cartilage, either upwards or downwards, so that the trunk 

 may remain undivided till it is beyond the os hyoides, or end in branches 

 opposite the cricoid cartilage. The division beyond the usual place is 

 more frequent than the branching short of that spot. It may ascend as 

 an undivided trunk (though very rarely), furnishing offsets to the neck 

 and head. 



In close contact with the oujex sjde of both the common and the internal 

 carotid artery, and incased in a sheath of fascia with them, is the large 

 internal jugular vein, which receives branches in the neck corresponding 

 with some of the branches- of the superficial artery. In some bodies the 

 vein may cover the artery , and the branches joining it above may form a 

 kind of plexus over the upper part of the common carotid. 



Nerves in the space. In connection, more or -less intimate, with the 

 large vessels, are the following nerves with a longitudinal direction : In 

 front of the sheath lies the descending branch of the hypo-glossal nerve ; 

 within the sheath, between the carotid artery and jugular vein, is the 

 pneumogastric nerve; and behind the sheath is the sympathetic nerve. 

 Along the outer part of the vessels the spilial accessory nerve extends for 

 a short distance, till it pierces the sterno-mastoid muscle. 



Several nerves are placed across the vessels : thus, directed transversely 

 over the two carotids, so as to form an arch below the digastric muscle, is 

 the hypoglossal nerve, which gives downwards its branch (descendens noni) 

 most commonly in front of the sheath. Appearing on the inner side of the 

 carotid arteries, close to the base of the space, is the glosso-plmryngcnl 

 nerve, which courses forwards between them. Inside the internal carotid 

 artery, opposite the hyoid bone, the superior laryngeal nerve comes into 



