430 PHYSIOLOGY 



In the upper part of the pons we find the fifth nerve (Fig. 196) 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 

 Kolando, 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 system. 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 quadrigemina. 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 



FIG. 196. Diagram showing cen- 

 tral connections of fifth nerve. 

 (CAJAL.) 



A, Gasserian ganglion ; B, acces- 

 sory motor nucleus ; c, main , . , . . . , 

 motor nucleus; D, facial nucleus; median line in the ventral part of the 



central grey matter, corresponding in 

 situation to the sixth and twelfth 

 nerves lower down. 



E, nucleus of hypoglossal; 

 p, sensory nucleus of fifth nerve; 

 o, cerebral tract (fillet) of fifth 

 nerve. 



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 systems of nuclei and conducting paths), which have 

 arisen in consequence of the great complexity of reaction required of 

 the nerve mechanisms in connection with the organs of special sense. 

 We must confine ourselves here to little more than the enumeration 

 of the chief masses, though we shall have occasion to refer to some in 

 rnore detail when dealing with the co-ordinating mechanisms of the 



