xi NERVES 533 



posterior of which are opposite 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), supplying 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 supplied the muscles of the tongue, as well as certain 

 muscles of the neck. 



Tho origin and distribution of the first ten pairs of cerebral 

 nerves correspond in their main features with those seen in 

 the frog (p. 163). The facial is almost entirely a motor 

 nerve and is chiefly important in supplying the facial mus- 

 cles, which a.re 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 con- 

 necting 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 

 or solar plexus being present close to the origin of the 

 anterior mesenteric artery. 



Sensory Organs. The sense of touch is situated in 

 microscopic tactile organs in the skin, and groups of cells, 



