MEDULLA OBLONGATA 



171 



3. Cranial Nerves 



(The physiology of these should be studied ivhile dissecting 

 them.} The nerves springing from and entering the medulla 

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

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

 sidered 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 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. 86. In the cranial nerves no sharp differentiation into 

 ventral and dorsal roots can be made out. Nevertheless 

 they contain the same component elements as the spinal 

 nerves, the fibres running either together or separately. 



FIG. 86. The Nuclei and Roots of the Cranial Nerves. (After EDINGER.) 



Ingoing Fibres. Somatic and splanchnic fibres (p. 158) 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 sixe, and by 

 forming synapses before their final distribution. 



The XII. (Hypoglossus) is purely a ventral 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 dorsal and partly of ventral 

 root fibres. The vagus is the great ingoing nerve from the 

 abdomen, thorax, larynx, and gullet, while, by outgoing fibres, 

 passing through it or through the accessorius, it is augmentor 



