PHYSIOLOGY OP THE POSTERIOR PITUITARY. 509 



by stimulation of the motor areas of the cortex are manifestations 

 of activity of the lower or central brain, incited therein ly sensory 

 impulses from these cortical areas. 



What constitutes this middle brain? The co-ordination, 

 so evidently preserved in animals deprived of their hemi- 

 spheres, points to the cerebellum as a possible member of the 

 group of organs to be considered in this connection. Includ- 

 ing this organ, therefore, and beginning with the anterior 

 structures, we would now have: the posterior pituitary body; 

 the infundibulum; the central gray matter, forming "a bed 

 for the development of the nuclei of the cranial nerves"; the 

 tegmental system, i.e., the reticular formation in the medulla 

 continued to the subthalamic region, and to which belong the 

 red nucleus and other bulbar nuclei. All this forms what 

 Professor Foster characterizes as "a more or less continuous 

 column of gray matter" connected with the spinal cord by 

 various ties, besides being, as it were, "a continuation of the 

 spinal gray matter." It is as evident that the optic thalami and 

 corpora quadrigemina are also members of the group, since 

 these related organs appear to be necessary for the success of 

 the experiment in which both cerebral hemispheres are re- 

 moved. Thus, referring to the frog, Foster says: "In this 

 animal it is comparatively easy to remove the cerebral hemi- 

 spheres, including the parts corresponding to the corpora 

 striata, leaving behind, intact and uninjured, the optic thalami 

 with the optic lobes, the representatives of the corpora quad- 

 rigemina, the small cerebellum, and the bulb. If the animal 

 be carefully fed and attended to, it may be kept alive for a 

 very long time: for more than a year, for instance." 



If, with this list before us, we now examine the annexed 

 illustration, originally from His's work, and, therefore, not 

 recently drawn, a rather suggestive coincidence appears, indi- 

 cating, perhaps, a total independence, in the embryo, of the 

 region containing all the structures enumerated from the 

 vesicle which subsequently develops into the hemisphere of 

 the same side. In mammals the latter is at first insignificant, 

 but it develops very rapidly, soon overlapping the middle 

 structures. The outline of the latter is colored bluish gray. 

 The name of each part is given on the cut: a feature that will 



