636 THE BRAIN. 



masses of gray 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 con- 

 tinuous column of gray matter, comparable to the gray matter of the spinal 

 cord, serves as a sort of backbone to the rest of the central nervous system. 

 With the spinal cord it is connected by various ties, besides being, as it 

 were a continuation of the spinal gray matter, and around it are built up 

 the great mass of the cerebrum, and the smaller but still larger mass of 

 the cerebellum ; the less important corpora quadrigemina we may for sim- 

 plicity's sake neglect. 



At the hind end we find various parts of the spinal cord becoming con- 

 nected 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 anter'o-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), con- 

 nected with the thalamus and other parts of the tegmental system ; and 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 are in a measure lost in the tegmen- 

 tum, 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 of the gracile and cuneate nuclei. To all 

 parts of the cerebral cortex it appears to be joined by those conspicuous 

 strands of the pedal system which end in the pons, and there make connec- 

 tions with the fibres of the middle peduncle. And we may here perhaps 

 remark that while this connection between the cerebrum and cerebellum is 

 wholly a crossed one, each cerebral hemisphere being joined with the oppo- 

 site half of the cerebellum, the connections between the spinal cord and the 

 cerebellum are largely uncrossed ones, that by the cerebellar tract being 

 wholly uncrossed, and that with the posterior column by the relay of the 

 gracile and cuneate nuclei being in part uncrossed. 



Thus the cerebral cortex has a double hold, so to speak, on the rest of 

 the central nervous system, first through the tegmental system, and secondly 

 through the cerebellar junction. But in addition to this there is another 

 tie between the cerebral cortex and the whole length of the cerebro-spinal 

 axis, or at least between it and the whole series of motor mechanisms in 

 succession from the nucleus of the third nerve to the nucleus, if we may so 

 call it, of the anterior root of the coccygeal nerve, namely, the great pyram- 

 idal tract, which thus appears as a something superadded to all the rest of 

 the central nervous system. 



When the cerebral hemispheres are removed this pyramidal tract falls 

 away, as does also the pedal system leading from the cerebrum to the pons, 

 but there still remains the tegmental system with its cerebellar and other 



