MEMBRANES OF BRAIN IN MAMMALIA. 145 



results. The human brain is exceeded in weight by that of the 

 Elephant and the Whale, but is absolutely heavier than in all 

 other animals. In the proportionate size of the cerebrum to the 

 cerebellum the human brain surpasses that of all Mammalia : it is 

 as 8 to 1. 



The brain in some individuals distinguished for intellectual 

 power has been found of unusual size, and remarkable for the 

 number and depth of the cerebral convolutions: the brain of 

 Cuvier weighed upwards of 64 oz. The superficies of the 

 cerebrum of the mathematician Gauss was estimated by Wagner 

 at 341 square inches, while that of an ordinary wage-man was 

 291 inches. 



We know not the size of brain in the Melanian inventor of the 

 ' throwing-stick,' or of that of the deductive observer of the pro- 

 perties of the broken branch bent at the angle of the ( boomerang.' 

 Such benefactors of their race were, perhaps, as superior to ordi- 

 nary Australians in cerebral development, as the analogous rare 

 exceptions in intellectual power have been found to be among 

 Europeans. 1 



§ 210. Membranes of the Brain. — The encephalon, like the 

 myelon, is immediately invested by an areolo-vascular tunic 

 called ( pia mater : ' it adheres to and follows all the foldings of 

 the surface, is continued into the ventricles, and there forms 

 processes called ' velum interpositum ' and ( choroid plexus.' It is 

 the area on which the vessels undergo the requisite degree of 

 diminution for penetrating the cerebral substance ; and, when with- 

 drawn, the proportion of such vessels pulled out of that substance 

 gives the flocculent appearance of the inner surface of the mem- 

 brane which Anthropotomy calls f tomentum cerebri.' 



The movements of the brain are served by a delicate serous 

 sac, called the ' arachnoid.' The outermost membrane, called 

 * dura mater,' adheres to the inner surface of the cranium, and 

 consists of a dense inelastic fibrous tissue. It sends a process 

 or duplicature inwards between the cerebrum and cerebellum 

 called ' tentorium,' and a second between the cerebral hemi- 

 spheres called 'falx.' In the Ornithorhynchus a bony plate 

 extends from the cranium into the falx (vol. ii. p. 323, fig. 

 204, b). A ridge of bone extends a short way into the ten- 

 torium in some marsupials : it is thin in Kangaroos and Phal angers, 

 thick in Thylacines, but of less extent here than in the Wolf, 

 (vol. ii. p. 504). In the Cachalot a bony plate projects from the 



1 Tables of size and weight of Mammalian brains will be found in xn, xli", 

 xxxii". 



VOL. III. L 



