STUDY OF BRAIXS OF SIX EMINENT SCIENTISTS AND SCHOLARS. 219 



Above this the axial fibers divide into two bundles called the cerebral crura, one to 

 the left and the other to the right ; and spreading forwards and outwards go to form 

 (in part) the cerebral hemispheres, on the sui-face of which is a layer of gray substance, 

 the cerebral cortex. The white portion is made up of conducting nerve-fibers, the 

 gray is the sentient and reacting mass containing numerous nerve-cells from which the 

 fibers arise. Many fibers pass to otlier regions of the gray matter within the hemi- 

 cerebrum on one side, and also, by means of commissures, to the hemicerebrum of the 

 other side. Of these commissures the callosum is the largest and most important ; it 

 is a bundle of white fibers which is largest in the brain of man, smallest (or onl)' just 

 beginning to develop) in the Marsupial and entirely absent in the lower animals. 



In the embryo the cerebro-spinal axis begins as a simple tube of nervous tissue, 

 but in the course of development and growth, especially among the higher vertebrates, 

 various segments undergo thickening, expansion, elongation and flexion. It is the 

 enlargement of the brain which causes the formation of the headbend together with 

 the marked modifications in the skull. Some of the encephalic segments are but 

 slightly modified, others become metamorphosed into complex and important struc- 

 tures, while the cavity of the neural tube is represented by the ventricles of the brain 

 and the narrow spinal canal. The most striking specialization in the Primate brain is 

 seen in the cerebral parts. No contrast could be greater than is to be seen in the com- 

 parison of the tiny cerebral appendage of the " olfactory brain " of the earliest verte- 

 brates with the huge cerebral mantle and dwindled olfactory apparatus in the Anthro- 

 pomorpha. This remarkable expansion of the cerebral hemispheres with which man 

 does his thinking is the latest development in the evolution of the brain. If we study 

 brains arranged in phyletic series, say from the fishes through the reptiles and birds to 

 the mammals of low and high order, we see the other segments of the brain progres- 

 sively overlapped by the cerebral hemispheres until we find in the brain of man that 

 supremacy in size and complexity of thought-apparatus which so distinguishes him 

 from other species. The amplified development of the special senses and of the 

 locomotive organization has involved the augmentation of coordinating systems. Thus 

 the synchronous development of the hand and the intellectual faculties has been one 

 of the most important factors in the forming of the massive brain which places man 

 at the head of animal creation. 



Perhaps no theme in all the natural sciences interests us so much as our kinsliip 

 with the ape. Proofs of the blood-relationship uniting man and monkey abound on 

 all sides and a general agreement as to man's place in the zoological system seems 

 permanently fixed. But in the mental powers of the Anthropomoi'pha (true apes) in 

 particular we see their kinship with man shown quite as much as in their physical 



