CHAP. IL] THE BRAIN. * 1113 



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 purpose 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 638 

 is done away with. The probable connection of the posterior 

 corpora quadrigemina with hearing is also interesting 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 ( 638), 

 which it possesses when the section passes in front of the optic 

 lobes ; and injury to the optic lobes produces incoordination of 

 movement and often " forced movements." It has been maintained 

 that the loss of coordination is in these cases due to removal of or 

 injury to the central grey matter in the walls of the third 

 ventricle, and not to mere removal of or injury to the optic 

 lobes ; but the whole evidence goes to shew that in the frog and 

 in the bird the optic lobes do play a part in the coordination of 

 movement, though lesions of the central grey 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 

 quadrigemina 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, however, is in most instances very 

 temporary. The connection of the anterior pair with vision 

 suggests a clue as to how this pair takes part in coordination ; 

 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 will often cause a person to reel, further admit that 

 purely auditory impulses, as distinct from what we have called 

 ampullar impulses, may take part in the general coordination of 

 bodily movements and in the maintenance of equilibrium, as they 

 certainly do in the special coordination of laryngeal movements, 

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

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



