158 HUMAN PHYSIOLOGY 



less definite mass of cells. The ingoing fibres generally form 

 synapses with cells 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. 85. In the cranial 

 nerves no sharp differentiation into anterior and posterior 

 roots can be made out, but they contain the same component 

 elements as the spinal nerves, the fibres running either 

 together or separately. 



Ingoing Fibres. Somatic and splanchnic enter the medulla 

 and have their cell stations in ganglia upon the nerves. 



Outgoing Fibres. Somatic and splanchnic pass out, the 



FIG. 85. The Nuclei and Roots of the Cranial Nerves. (After EDINGER.) 



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) is essentially the posterior root of the XI. 

 (Spinal Accessory), but it transmits some outgoing fibres. 

 It is the great ingoing nerve from the abdomen, thorax, 

 larynx, and gullet, while, by outgoing fibres passing through 

 the vagus or accessorius, it is augmentor for the muscles of 

 the bronchi and alimentary canal, inhibitory to the heart, 

 dilator to blood-vessels of the thorax and abdomen, and 

 motor to the muscles of the larynx and to the levator palati. 

 The accessorius is also motor to the sterno-cleido-mastoid 

 and trapezius. 



The IX. (Glossopharyngeal) is essentially a posterior root, 

 and is the ingoing nerve for the back of the mouth, the 

 Eustachian tube, and tympanic cavity. It transmits out- 



