380 



PHYSIOLOGY 



nucleus. From the latter a distinct band of fibres passes up to the cere- 

 bellum, forming the median division of the restiform body, while other fibres 

 run across to the tegmentum of the opposite side, where they take part in the 

 formation of the posterior longitudinal bundle. 



In a section through the fourth ventricle through the middle of the pons, 



a group of large cells is seen in the position 

 occupied by the nucleus of the hypoglossal 

 below. These cells give rise to the fibres of 

 the sixth nerve. Another group is seen lying 

 laterally and more deeply, evidently belong- 

 ing to the lateral horn system. This is the 

 nucleus of the seventh or facial nerve, the 

 fibres of which pass dorsally and anteriorly, 

 looping round the sixth nerve-nucleus, before 

 issuing as the root of the seventh nerve 



In the upper part of the pons we find the 

 fifth nerve (Fig. 195) with its two roots. 

 The fibres of the sensory root derived from 

 the cells of the Gasserian ganglion bifurcate. 

 The upper divisions, which are short, end in 

 a mass of grey matter at the lateral part of 

 the formatio reticularis, the so-called sensory 

 root, while the descending divisions form a 

 long strand of white fibres passing down as. 

 far as the second cervical nerve and lying 

 over the substantia gelatinosa of Rolando, 

 around the small cells of which the fibres 

 finally terminate. The motor fibres arise 

 partly from the motor nucleus, a mass of 

 cells lying internally to the sensory nucleus, 

 and belonging probably to the lateral horn 

 A large number are derived from 

 a long column of cells, which stretches 

 forward from the nucleus as far as the level 

 of the anterior corpora quadrigeinina. 

 These fibres are known as the descending 

 motor root of the fifth nerve. 



In the region of the mid-brain, besides the root of the fifth nerve just 

 mentioned, we find only the motor nuclei of the third and fourth nerves, 

 which are situated near the median line in the ventral part of the central grey 

 matter, corresponding in situation to the sixth and twelfth nerves Imvrr 

 down. 



INTERMEDIATE GREY MATTER OF THE CEREBRAL AXIS 



The masses of grey matter which are found throughout this region may 

 be regarded as extra shunting stations (or association centres for various 



FIG. 195. Diagram showing cen- 

 tral connections of fifth nerve. 

 (CAJAL.) 



A, Gasserian ganglion ; B, acces- system 

 aory motor nucleus ; c, main motor * 

 nucleus ; D, facial nucleus; E, nucleus 

 if hypoglossal ; F, sensory nucleus of 

 fifth nerve ; G, cerebral tract (fillet) 

 of fifth nerve. 



