THE MACHINERY OF COORDINATED MOVEMENTS. 651 



and wholly abnormal position of the eyes, which alone might perhaps explain 

 many of the phenomena. 



559. The phenomena presented by animals deprived of their cerebral 

 hemispheres show that this machinery of coordination is supplied by cerebral 

 structures lying between the cerebral hemisphere above and the top of the 

 spinal cord below. But when we ask the further question, How is this 

 machinery related to the various elements which go to make up this part 

 of the brain ? the only answers which we receive are of the most imperfect 

 kind. 



In the case of the frog we can, after removal of the cerebral hemispheres, 

 make an experimental distinction in the parts left between the optic thalami 

 with the optic nerves and tracts, the optic lobes, and the bulb with the rudi- 

 mentary cerebellum. When the optic thalami are removed, as might be 

 expected, the evidence of visual impressions modifying the movements of 

 the animal disappears ; and it is stated that apparently spontaneous move- 

 ments are much more rare than when the thalami are intact. When the 

 optic lobes as well as the cerebral hemispheres are removed, the power of 

 balancing is lost ; when such a frog is thrown off its balance by inclining 

 the plane on which it is placed, it slips back or falls down ; the special co- 

 ordinating mechanism for balancing must, therefore, in this animal have a 

 special connection with the optic lobes. But after removal of these organs 

 the animal is still capable of a great variety of coordinate movements ; 

 unlike a frog retaining its spinal cord only, it can swim and leap, it main- 

 tains a normal posture, and when placed on its back immediately regains 

 the normal posture. The cerebellum of the frog is so small, and in re- 

 moving it injury is so likely to be done to the underlying parts, that it 

 becomes difficult to say how much of the coordination apparent in a frog 

 possessing cerebellum and bulb is to be attributed to the former or to the 

 latter ; probably, however, the part played by the former is small. 



In the case neither of the bird nor of the mammal have we any exact 

 information as to the behavior of the animal after removal of the parts 

 behind the hemispheres, in addition to the hemispheres themselves. Our 

 knowledge is confined to the results of the ablation or of the stimulation of 

 parts, the cerebellum for instance, in animals in which the rest of the brain 

 has been left intact. Observations of this kind have disclosed many inter- 

 esting facts, besides the forced movements just referred to, but they have not 

 led to, and indeed could hardly be expected to lead to, any clear views as to 

 the point which we are now discussing. It does not follow that every part, 

 injury or stimulation of which interferes with coordinated movements, or 

 gives rise to definite, forced, or other movements, is to be considered as part 

 of the machinery under consideration. The corpora striata and cerebral 

 hemispheres form, as we have seen, no part of the machinery, yet injury to 

 them may disorder the machinery ; and the fact that removal of or injury 

 to the cerebellum disorders the machinery is no proof by itself that the cere- 

 bellum is an essential part of the machinery. 



If we may trust to deductions from structural arrangements, we might 

 be inclined to infer that the anatomical relations of the tegmental region 

 from the bulb upward point to its serving 'as the foundation of the machin- 

 ery in question. Behind it has full connections with various parts of the 

 cord, while in front by means of the optic thalami and anterior corpora 

 quadrigemina, if not by other ways as well, it is so far associated with the 

 optic nerves that the path seems open for visual impulses to gain access to 

 it. To this foundation, however, we must add the cerebellum, on account of 

 its relations to it, to the cord, and to the bulb through the restiform bodies, 

 including its ties with the auditory nerve. And if we add the cerebellum 



