86 



NEKVES. 



nervus communicans faciei or respiratory nerve of the face, distributed 

 to the muscles of the face ; the acoustic nerve, auditory nerve or portio 

 mollis of the seventh pair, which passes to the organ of hearing ; the 

 eighth pair, pneumogastric, par vagum or middle sympathetic, which is 

 dispersed particularly on the larynx, lungs, heart, and stomach ; the 

 glosso-pharyngeal, often considered as part of the last, and whose name 

 indicates its distribution to the tongue and pharynx ; the great hypo- 

 glossal, ninth pair or lingual nerve distributed to the tongue ; and the 

 spinal accessory of Willis, which arises from the spinal cord in the cer- 

 vical region; ascends into the cranium, and issues by one of the fora- 

 mina to be distributed to the muscles of the neck. All these proceed, 

 perhaps, from the medulla oblongata; the brain and cerebellum not 

 furnishing one. 



The spinal nerves are thirty in number on each side. They make 

 their exit by the intervertebral foramina, and are divided into eight 

 cervical, twelve dorsal, five lumbar, and five or six sacral. 



The encephalic nerves are irregular in their formation, and, with the 

 exception of the fifth pair, originate from one root. Each of the spinal 

 nerves arises from two fasciculi, the one anterior, and the other poste- 

 rior : these roots are separated from each other by the ligamentum 

 denticular *e; but they unite beyond this ligament, and near the inter- 

 vertebral foramen present one of those knots, known under the name 

 of ganglions or ganglia, in the formation of which the posterior root 

 is alone concerned. 



When the nerves have made their exit from the cranium and spine, 



they proceed to the organs to which 

 they have to be distributed; ramifying 

 more and more, until they are ultimately 

 lost sight of, even when vision is aided 

 by a powerful microscope. It is not 

 positively decided, whether the nervous 

 fibres have any distinct terminations 

 either in the nervous centres, or in the 

 organs to which they are distributed. 

 In the gray matter of the brain of the 

 vertebrata, they would appear to form 

 a kind of plexus of loops ; and the ulti- 

 mate fibres do not seem to anastomose. 

 The following has been described as the 

 mode in which the nervous fibres are 

 generally distributed to the peripheral 

 organs. The trunks subdivide into 

 small fasciculi, each of which consists 

 of from two to six fibres, and these form 

 plexuses, whose arrangement bears a 

 general resemblance to that of the ele- 

 ments of the tissue in which they are 



Terminal nerves, on the sac of the second placed. The primitive fibres then 86- 



molar tooth of the lower jaw, in the sheep ,- parate \ and each, after passing over 



showing the arrangement in loops. (After * ' .. . 



Valentin.) several elementary parts of the contain- 



Fig. 16. 



