590 COMPARATIVE PHYSIOLOGY. 



served in the cranial region of the vertebrate, as shown by the 

 nerves themselves. 



The afferent fibers of both splanchnic and somatic nerves 

 pass into the spinal ganglion, situated in the nerve-root, which 

 may be regarded as stationary. 



It is different with the anterior roots. Some of the fibers 

 are not connected with ganglia at all ; others with ganglia not 

 fixed in position, but occurring at variable distances from the 

 central nervous system (these being the so-called sympathetic 

 ganglia) : thus, the anterior root-fibers are divisible into two 

 groups, both of which are efferent, viz., ganglionated and non- 

 ganglionated. The ganglionated belong to the splanchnic sys- 

 tem, and have relatively small fibers; the non-ganglionated 

 include both somatic and splanchnic nerves, composing the 

 ordinary nerve-fibers of the voluntary striped muscles of res- 

 piration, deglutition, and locomotion. 



It would appear that these now isolated ganglia have been 

 themselves derived from a primitive ganglion mass situated on 

 the spinal nerves; so that the distinction usually made of gan- 

 glionated and non-ganglionated roots is not fundamental. 



A spinal nerve is, then, formed of — ^1. A posterior root, the 

 ganglion of which is stationary in position, and connected with 

 splanchnic and somatic nerves, both of which are afferent. 2. 

 An anterior root, the ganglion of which is vagrant, and con- 

 nected with the efferent small-flbered splanchnic nerves. 



Among the lower vertebrates both anterior and posterior 

 roots pass into the same stationary ganglion. Such is also the 

 case in the first two cervical nerves of the dog. 



Does the above-mentioned plan of distribution, etc., hold for 

 thes cranial nerves ? 



■Leaving out the nerves of special sense (olfactory, optic, and 

 auditory), the other cranial nerves maybe thus divided: 1. A 

 foremost group of nerves, wholly efferent in man, viz., the 

 third, fourth, motor division of the fifth, the sixth, and seventh. 

 2. A hindmost group of nerves of mixed character, viz., the 

 ninth, tenth, eleventh, and twelfth. 



The nerves of the first group, since they have both large- 

 flbered, non-ganglionated motor nerves, and also small-flbered 

 splanchnic efferent nerves, witli vagrant ganglia (ganglion 

 oculomotorii, ganglion geniculatum, etc.), resemble a spinal 

 nerve in respect to their anterior roots. They also resemble 

 spinal nerves as to their posterior roots, for at their exit from 



