720 THE BRAIN, 



inoval of or injury to the central gray matter in the walls of the third ven- 

 tricle, and not to mere removal of or injury to the optic lobes ; but the 

 whole evidence goes to show that in the frog and in the bird the optic lobes 

 do play a part in the coordination of movement, though lesions of the cen- 

 tral gray matter around the third ventricle, or, indeed, of the thalamus or 

 other parts of the tegmentum, may give rise to loss of coordination or to 

 " forced movements." 



In the mammal removal of or injury to the posterior corpora quadri- 

 gemina does not cause blindness, but may, like a lesion of the anterior pair, 

 give rise to loss of coordination or to forced movements ; the effect, how- 

 ever, is, in most instances, very temporary. The connection of the anterier 

 pair with vision suggests a clew as to how this pair takes part in coordina- 

 tion ; but as to how the posterior pair could intervene in the matter we have 

 hardly so much as a hint ; for, even if we admit a connection between them 

 and the sense of hearing, and, remembering that a loud sound would often 

 cause a person to reel, further admit that purely auditory impulses, as dis- 

 tinct from what we have called ampullar impulses, may take part in the 

 general coordination of bodily movements and in the maintenance of equi- 

 librium, as they certainly do in the special coordination of laryngeal move- 

 ments, still we are not much nearer an understanding of the matter. We 

 may add that section of the lateral fillet, which appears as a conspicuous tie 

 between the posterior corpora quadrigemina and the parts of the nervous 

 system behind them, does not appear to have any marked effect in produ- 

 cing incoordination. 



In fine, beyond the broad facts on which we dwelt in a previous section, 

 namely, that we maintain our equilibrium and carry out complex movements 

 involving often several parts of our body, through what we call coordination, 

 that afferent impulses supply important factors of this coordination, and 

 that the cerebellum, through the vestibular nerves in part at all events, 

 together with other portions of the middle brain, are in some way its chief 

 instruments, we as yet know very little. We have certainly no adequate 

 knowledge as to how either pair of corpora quadrigemina exactly intervene 

 in the matter, or, indeed, as to what other parts they play in the general 

 work of the brain. 



With regard to other tracts of fibres or areas of gray matter we have 

 nothing to say, except as regards those which are more or less immediately 

 connected with certain of the cranial nerves, such for instance as the nerves 

 for movements of the eyes, and these it will be best to consider when we have 

 to deal with the nerves themselves. 



601. Besides the somatic functions which in previous discussions we 

 have chiefly had in view, the brain as a whole undoubtedly carries out 

 splanchnic functions ; concerning these, however, we must be very brief. 



Of the respiratory and vasomotor functions of the bulb we have already 

 treated in their appropriate places, and we have referred ( 449) to the 

 experimental evidence that a lesion of the corpus striatum or of the front 

 part of the optic thalamus has a remarkable influence on the development 

 of heat in the body. We have further seen that the higher parts of the 

 brain, acting through the bulb, exercise powerful influences on respiration, 

 on the vasomotor system, and on the beat of the heart. Daily experience 

 affords abundant instances of actions such as these, as well as of the influence 

 of the brain on other organic functions. We can bring our will to bear on 

 the mechanism of micturition ( 364) which is almost wholly, and on the 

 mechanism of defecation ( 236) which is largely, splanchnic in nature. 

 These movements, however, are not skilled movements ; and as we explained 

 in dealing with them, the action of the brain as regards them seemed limited 



