626 NERVOUS SYSTEM 



ventral muscles between the pelvis and tail, together with those of 

 the cloacal region and the copulatory organs. 



The dorsal branches of all the spinal nerves in the whole pelvic 

 region are restricted to small, cutaneous branches in conformity with 

 the reduction of the dorso-spinal muscles. The caudal nerves are 

 also small, their dorsal branches supply the levator and their 

 ventral the depressor muscle of the tail. 



III. The Cranial or Cerebral Nerves have been already described 

 (BRAIN). 



IV. The Sympathetic System consists of the visceral branches of 

 the Cerebro-Spinal Nerves, and supplies chiefly the alimentary and 

 genital organs and the circulation. The Nerves composing it have 

 no axial cylinder : they are paler than the white fibres, and are 

 characterized by the presence of ganglia in their course, each 

 branch containing one near its base which beside sending off 

 other ramifications is connected with the corresponding ganglion of 

 the next metamere, so as to form a " Sympathetic" chain running 

 along each side of the ventral surface of the vertebral column. 

 The two chains by means of these connexions somewhat resemble 

 a ladder, the cross-bars of which are called rami communicantes, 

 from a mistaken notion that they join the longitudinal " strand" 

 or n. sympathicus of their side with the medulla, the fact being 

 that the cross-bars are the true " rests," the lateral strands rather 

 making the connexion between the successive ganglia. In the 

 region of the NECK each of these strands runs, accompanied by 

 the vertebral artery of its side, through the transverse foramen of 

 each of the cervical vertebrae. In the thoracic region each strand 

 is double, and the basal ganglia are successively connected with the 

 next by a nervous branch which runs over the head of the rib, and 

 by another which passes directly through the space between the 

 head of the rib and its tubercle. In the pelvic region each strand 

 again becomes single ; but, conversely to the single strand of the 

 cervical region, each is composed of ventral branches only, while 

 lastly in the caudal region the right and left branches approach 

 and coalesce in the middle line. From the first thoracic ganglion 

 there issues a cardiac branch supplying the HEART, while other 

 branches starting from neighbouring ganglia form a sort of plexus 

 which, accompanying the cceliac artery, innervate the stomach, LIVER 

 and other viscera. Similar branches from the basal ganglia of the 

 lumbar and sacral regions form a plexus with ganglia numerously 

 interspersed, and serve the rest of the Alimentary Canal, the 

 KIDNEYS (page 480), genital organs and CLOACA (page 90), where 

 they partly anastomose with the branches of the Pudic portion of 

 the Sacral Plexus. 



From the first pair of cervical ganglia the Sympathetic strands 

 are continued on either side to the ganglia of the n. hypoglossus, 



