970 INTERMEDIATE GREY MATTER. [BOOK in. 



many detached portions of grey matter, corresponding to some 

 part of the anterior horn of the spinal cord. Whether they are 

 exactly homologous to the hypoglossal nucleus, and their fibres 

 to simple anterior roots, is not so clear. 



Lastly, the auditory nerve, both from its character as a nerve 

 of special sense and from the remarkable features of its nuclei, is 

 even more difficult. Most probably it results from the fusion of 

 more roots than one ; but it is impossible at present to obtain a 

 clear conception of the nature of the whole nerve. 



2. The Superficial Grey Matter. 



625. The whole of the surface of each cerebral hemisphere 

 for some little depth inwards consists of grey matter, possessing 

 special characters ; this is called the cortical grey matter, or the 

 cortex cerebri, or shortly and simply the cortex. As we shall see, 

 by its histological and still more by its physiological features, it 

 stands apart from all other kinds of grey matter. 



The whole of the surface of the cerebellum is also covered with 

 grey matter, which, while possessing features of its own, so far 

 resembles the cerebral cortex in its histological characters that 

 it too has been spoken of as cortex, as the cortex cerebelli. By 

 its functional manifestations, however, it differs widely from the 

 cerebral cortex ; and since there are many advantages in being 

 able to use the word cortex in connection with the cerebrum 

 only, it is desirable not to speak of a cerebellar cortex but to 

 employ the term " superficial grey matter of the cerebellum." 



The third ventricle and the hinder part of the fourth ventricle 

 are not roofed in by nervous material, and possess no superficial 

 grey matter at all. In the corpora quadrigemina, which form the 

 roof of the aqueduct or cavity of the mid-brain, grey matter is 

 present and possesses, in the case of the anterior corpora quadri- 

 gemina at least, characters to a certain extent analogous to those 

 of the cortex and to the cerebellar superficial grey matter ; but it 

 will be best to consider the grey matter of these bodies as 

 belonging to another category. 



3. The Intermediate Grey Matter of the Crural 

 System. 



626. We have seen ( 603) that the crura cerebri form the 

 prominent part of a system of longitudinal fibres stretching from 

 each cerebral hemisphere to the bulb and to the spinal cord. 

 This system of fibres, upon which we may consider the various 

 parts of the brain to be as it were founded, we may speak of 

 as the crural system. It is, it is true, not one continuous strand, 

 but a number of different strands, having different beginnings 



