382 



PHYSIOLOGY 



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 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 median line in the ventral part of the 

 > x^Ht^ - -K central grey matter, corresponding in situa- 

 / 1 tion to the sixth and twelfth nerves lower 



down. 



INTERMEDIATE GREY MATTER OF 

 THE CEREBRAL AXIS 



The masses of grey matter which are 

 found throughout this region may be re- 

 garded as extra shunting stations (or associa- 



FIG. 195. Diagram showing cen- 



tral connections of fifth nerve, tion centres for various systems of nuclei and 

 ganglion; B, acces- conducting paths), which have arisen in con. 



, 

 sory motor nucleus ; c, main motor sequence of the great complexity of reaction 



oTh y ^ll f"?rnururo? ^quired of the nerve mechanisms in connec- 

 fifth nerve; G, cerebral tract (fillet) tion 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 more detail when dealing with the co-ordinating 

 mechanisms of the cerebral axis. From below upwards we may enumerate 

 the following grey masses : 



In the medulla is the large olivary body, with the accessory olive lying on 

 its inner side. Each olive sends fibres across the middle line to the opposite 

 cerebellar hemisphere, and must be regarded as connected with this body 

 in its functions, since atrophy or removal of one side of the cerebellum is 

 followed by atrophy of the opposite olive. 



In the pons we find a similar but smaller body, the superior olive, in the 

 neighbourhood of the nucleus of the seventh nerve. The superior olive is 



