200 



VETERINARY PHYSIOLOGY 



CRANIAL NERVES. 



Although the cranial nerves contain both ingoing and 

 outgoing fibres, they may be dealt with at this point. Their 

 functions should be studied while they are being dissected. 

 They do not come off in the same regular fashion as do the 

 spinal nerves, although they, like the spinal nerves, must be 

 considered as forming part of the spinal arcs. The outgoing 

 fibres of each spring from a more or less definite mass of 

 cells. The ingoing fibres form synapses with cells generally 

 arranged in definite groups. In this way the so-called 

 nuclei of the cranial nerves are formed. The position of 

 these is indicated in fig. 100. In many of the cranial nerves 



Fig. 100.— The Nuclei and Roots of the Cranial Nerves. (After Edixger.) 



no sharp differentiation into anterior and posterior roots can 

 be aiade out. Nevertheless, they contain the same com- 

 ponent elements as the spinal nerves, the fibres running 

 either together or separately. 



Ingoing Fibres. — Somatic and splanchnic fibres (p. 54) 

 enter the medulla and have their cell stations in ganglia 

 upon the nerves. 



Outgoing Fibres. — Somatic and splanchnic fibres pass 

 out, the latter being characterised by their small size, and 

 by forming synapses before their final distribution. 



The XII. (Hypoglossus) is purely an anterior root nerve, 

 and is motor to the muscles of the tongue. 



The X. (Vagus) and the XI. (Spinal Accessory) are 

 practically one nerve, consisting partly of posterior and 



