xi NERVES 533 



and bulb by numerous fibres, the posterior of which are op- 

 posite the fifth spinal nerve, from which point it runs forwards 

 between the dorsal and ventral roots and leaves the skull 

 together with the glossopharyngeal and vagus (p. 496), sup- 

 plying certain muscles of the neck and shoulder. The 

 hypoglossal arises by a number of fibres from the ventral 

 surface of the bulb, passes out through the condylar foramen, 

 and supplies the muscles of the tongue as well as certain 

 muscles of the neck. 



The origin and distribution of the first ten pairs of cerebral nerves 

 correspond in their main features with those seen in the frog. The facial 

 is almost entirely a motor nerve and is chiefly important in supplying 

 the facial muscles, which are very highly developed in Mammals. An 

 anterior and a posterior or recurrent laryngeal nerve are given off from 

 the vagus. 



The relations of the sympathetic nerves (Fig. 135, sy) are 

 also essentially similar to those occurring in the frog (p. 162). 

 Each passes backwards along the neck close to the vagus 

 (vg) and alongside the carotid artery, enlarging to form an 

 anterior and a posterior cervical ganglion. In the thorax 

 it runs just beneath the heads of the ribs, having a ganglion 

 in each intercostal space : it then passes into the abdomen, 

 lying close to the centra of the vertebrae and having ganglia 

 at intervals. From all the sympathetic ganglia branches 

 are given off connecting them with the spinal nerves, others 

 going to the blood-vessels : others again, in the thorax and 

 abdomen, are connected with plexuses from which nerves 

 pass to the heart and abdominal viscera. In the abdomen 

 these plexuses can be seen in the mesentery, a large cceliac 

 plexus being present close to the origin of the cceliac and 

 mesenteric arteries. 



Sensory Organs. The sense of touch is situated in micro- 

 scopic tactile organs in the skin, and groups of cells, called 



