44 ANATOMY OF A CHELONIAN. 



their inner sides ; they then run along the neck to the 

 head. About half way up the neck they come into re- 

 lation Avith the sympathetic and pneuviogastric nerves^ and 

 the internal jugular vein. Trace each carotid, taking 

 great care of the nerves near its upper end, until it en- 

 ters the skull by a foramen (26, e)^ just in front of the 

 auditory capsule. 



98. As each carotid is dissected, the thymus gland 

 will be found — a loosely aggregated, yellowish mass, 

 near the base of the neck on each side, and internal to 

 the artery. 



99. It will be best to trace back the pneumogastric 

 nerves now, as their terminal branches are apt to be 

 injured in dissecting the aortic arches. Just behind the 

 hyoidean apparatus, the carotid artery has the vagus on 

 its outer, and the cervical sympathetic on its inner side. 

 For the present follow the nerves from the skull, be- 

 ginning about an inch and a half behind the cranium. 

 A short way from the head, the sympathetic comes into 

 close relation with the vagus, so that care is needed to 

 separate them ; finally, about opposite the fifth cervical 

 vertebra, the nerves separate, the sympathetic passing 

 out toward the axilla. 



100. Follow the left pneumogastric till it crosses the 

 left aorta ; at this point it gives off the recurrent laryn- 

 geal nerve^ which, turning round the aorta, runs up the 

 neck alongside the gullet. After giving off this branch, 

 the vagus stem breaks up into a leash of branches, some 

 of which run mesially toward the heart, while others 

 may readily be traced along the bronchus to the lung, 

 and to the ventral side of the stomach near the cardia. 



