MAMMALIA. 303 



sends a lingual branch to the tongue. The vagi run back along 

 the neck by the sides of the common carotids. Each gives off to 

 the larynx a superior laryngeal nerve, from which a depressor 

 branch runs, closely united with the sympathetic, to the heart. 

 At the posterior end of the neck a recurrent laryngeal nerve is 

 given off, which curves round the aorta on the left, or the sub- 

 clavian on the right, and runs forwards to the larynx. Behind 

 this the vagi run through the thorax and pierce the diaphragm, 

 finally breaking up into branches for the abdominal viscera. 



The spinal nerves arise by two roots as usual, and are named 

 cervical, thoracic, <fec.. according to the region of the vertebral 

 column to which they correspond. 



The last four cervical and the first thoracic nerves form the 

 orachial plexus, from which the fore-limb is supplied, and from 

 which also arises the phrenic nerve, which runs back to supply 

 the diaphragm. 



The lumbo-sacral plexus for the hind-limb is constituted by the 

 last three lumbar and the first three sacral nerves. 



(3) The sympathetic system is formed by a ganglionated cord 

 on each side (cf. p. 215) of the body, beginning in the head, 

 traversing the neck, and then running ventral to the vertebral 

 column through the thorax and abdomen into the tail. These 

 are connected by rami communicantes with some of the cranial 

 nerves and with the spinal nerves. They are also connected by 

 commissures with each other. In the neck there are only three 

 ganglia, the posterior and middle cervical at the root of the neck, 

 and the anterior cervical placed near and connected with the 

 vagus ganglion. In the thorax two large splanchnic nerves run off 

 from the cords, and, piercing the diaphragm, fuse with a large 

 cosliac ganglion, placed just in front of the origin of the anterior 

 mesenteric artery, and united with an anterior mesenteric ganglion 

 just behind it.* This latter ganglion is again connected with a 

 posterior mesenteric ganglion situated near the origin of the 

 posterior mesenteric artery. From these ganglia numerous 

 branches run off to the abdominal viscera. The sympathetic 

 also supplies the vascular system. 



10. Sense Organs (1) Tactile Organs. Numerous touch-cor- 

 puscles are present in the skin (p. 271), especially at the bases 

 of the vibrissae. 



* Cceliac ganglion + anterior mesenteric ganglion =semilunar ganglion of 

 .human anatomy. 



