CHAP. IL] THE BRAIN. 997 



The least conspicuous, but perhaps in point of origin the oldest 

 part of the brain, seems to be what we have called the central grey 

 matter. This seems to serve chiefly as a bed for the development 

 of the nuclei of the cranial nerves. 



Next to the central grey matter and more or less associated 

 with it comes what we have called the tegmental region, of which 

 the reticular formation, coming into prominence in the bulb and 

 continued on to the subthalamic region, forms as it were the core. 

 Belonging to the tegmental system are numerous masses of grey 

 matter from the conspicuous optic thalamus and the red nucleus 

 in front to the several nuclei of the bulb behind. This complex 

 tegmental system, which may perhaps be regarded as a more or 

 less continuous column of grey matter, comparable to the grey 

 matter of the spinal cord, serves as a sort of back bone to the rest 

 of the central nervous system. With the spinal cord it is con- 

 nected by various ties, besides being as it were a continuation of 

 the spinal grey matter, and around it are built up the great 

 mass of the cerebrum, and the smaller but still large mass of the 

 cerebellum; the less important corpora quadrigemina we may for 

 simplicity's sake neglect. 



At the hind end we find various parts of the spinal cord 

 becoming connected with this tegmental system, either passing 

 into it and becoming, as far as our present knowledge goes, lost in 

 it, or supplying strands or fibres which passing into it become 

 through it connected with other parts. Thus the anterior column 

 of the cord exclusive of the direct pyramidal tract, the lateral 

 column exclusive of the crossed pyramidal and cerebellar tracts 

 (and possibly the antero-lateral ascending tract), together with 

 part of the posterior column appear to join the tegmental system, 

 while part of the posterior column, after the relay of the gracile 

 and cuneate nuclei, passes through the system as the fillet destined 

 for various structures. 



At the front end we find all parts of the cerebral cortex 

 (though some regions, namely the temporo-occipital, to a greater 

 extent than others), connected with the thalamus and other parts 

 of the tegmental system ; and, as we have seen, the corpus 

 striatum may possibly possess like connections. 



^_ _! The relations of the cerebellum to this system are notable. On 

 the one hand the cerebellum is directly connected with the system, 

 partly by fibres which pass from the bulb to join the restiform 

 body or inferior peduncle, partly by the superior peduncles which, 

 as we have seen, are in a measure lost in the tegmentum, and partly 

 probably by fibres of the middle peduncles also making connections 

 with the tegmentum. On the other hand the cerebellum forms 

 around the tegmental system a great junction between the spinal 

 cord and the cerebrum. To the spinal cord it is joined in a 

 direct manner by the cerebellar tract and possibly by the antero- 

 lateral ascending tract, and in an indirect manner by the relay 



