OTHER ASPECTS OF THE FUNCTIONS OF THE BRAIN. 719 



in the pes, the view has gained ground that the tegmeutum is essentially a 

 sensory structure. But there does not appear to be adequate evidence either 

 clinical or experimental for such a conclusion. The thalamus, which we have 

 regarded as the front so to speak of the tegmentum, cannot, as we have 

 already urged ( 598), be considered exclusively or especially sensory. And 

 many of the ties of the tegmentum, such as the fibres from the corpora striata 

 ending in the substantia nigra, for this may be considered as properly be- 

 longing to the tegmentum, are of the kind which we may suppose to be 

 efferent or motor. Indeed, we may probably regard the whole tegmentum 

 as being broadly the analogue in the forward segments of the cerebro-spinal 

 axis of both the anterior and posterior gray matter of the spinal segments 

 behind. 



Though we are thus in the dark concerning what goes on in the cere- 

 bellum, it may be worth while to call attention once more to the remarkable 

 characters of the superficial gray matter ( 561). The many points of re- 

 semblance between it and the cerebral cortex cannot but suggest that the 

 processes taking place in it have some analogies with cortical events. And 

 it is, at least, a fact of some significance that congenital deficiency, or 

 atrophy of the cerebral hemisphere of one side, is frequently accompanied 

 by a corresponding deficiency of the crossed cerebellar hemisphere. 



600. Both the anterior and posterior corpora quadrigemina are com- 

 plex in structure ; not only do they differ from each other, but also in each 

 the gray matter differs in different parts, both as to its nature and appear- 

 ance and as to its connections with tracts of fibres. If we have little right 

 to speak of the " functions of the cerebellum," we have even less right to 

 speak of the " functions of the corpora quadrigemina " or of either pair of 

 them. The anterior pair, as we have seen, has to do in some way with 

 vision ; but we have reason to think that a part only of the whole body is 

 thus concerned ; and there is some foundation for the view that of this part 

 one portion belongs, so to speak, to the optic tract, and another portion to 

 the cortical fibres of the optic radiation. Possibly still another part is con- 

 cerned in bringing, as we have ( 586) suggested, visual impulses to bear on 

 the coordination of movements. 



Stimulation of the surface of the posterior pair, besides giving rise to 

 movements of various parts of the body, has in monkeys and some other 

 animals the singular effect of producing a vocal utterance in the form of a 

 cry or bark. But we cannot make much use of these results for the pur- 

 pose of drawing conclusions as to what share these bodies take in the whole 

 work of the brain. In the frog, the optic lobes correspond to the two pair 

 of corpora quadrigemina together ; and the cry just mentioned may, perhaps, 

 be put side by side with the fact that in the frog the optic lobes seem to 

 furnish a mechanism for croaking ; when the optic lobes are destroyed, the 

 reflex croaking mentioned in 551 is done away with. The probable con- 

 nection of the posterior corpora quadrigemina with hearing is also interest- 

 ing in this connection ; but we have no satisfactory evidence of any special 

 ties between the bodies in question and either the cortical area for phonation 

 or the vocal mechanism in general ; the occurrence of the cry remains so far 

 an isolated fact. 



In frogs, in which the cerebellum is very small, the optic lobes seem to 

 be particularly concerned in the coordination of movements. When the 

 brain is removed by means of a section behind the optic lobes the animal 

 loses the power of balancing itself ( 551), which it possesses when the sec- 

 tion passes in front of the optic lobes ; and injury to the optic lobes pro- 

 duces incoordination of movement and often "forced movements." It has 

 been maintained that the loss of coordination is in these cases due to re- 



