580 NERVOUS SYSTEM. 



The cerebellum (little brain or after brain) is situated in the inferior occipital 

 fossse, being separated from the under surface of the posterior lobes of the 

 cerebrum by the tentorium cerebelli. It is connected to the rest of the en- 

 cephalon by means of connecting bands, called crura : of these, two ascend to 

 the cerebrum, two descend to the medulla oblongata, and two blend together 

 in front, forming the pons Yarolii. 



The pons Varolii is that portion of the encephalon which rests upon the 

 upper part of the basilar process. It constitutes the bond of union of the 

 various segments above named, receiving, above, the crura from the cere- 

 brum; at the sides, the crura from the cerebellum; and below, the medulla 

 oblongata. 



The medulla oblongata extends from the lower border of the pons Varolii to 

 the upper part of the spinal cord. It lies beneath the cerebellum, resting on 

 the lower part of the basilar groove of the occipital bone. 



Weight of the encephalon. The average weight of the brain, in the adult male, 

 is 49^ oz., or little more than 3 Ib. avoirdupois; that of the female, 44 oz.; the 

 average difference between the two being from 5 to 6 oz. The prevailing 

 weight of the brain, in the male, ranges between 46 oz. and 53 oz. ; and, in the 

 female, between 41 oz. and 47 oz. In the male, the maximum weight out of 

 278 cases was 65 oz., and the minimum weight 34 oz. The maximum weight 

 of the adult female brain, out of 191 cases, was 56 oz., and the minimum weight 

 31 oz. It appears that the weight of the brain increases rapidly up to the 

 seventh year, more slowly to between sixteen and twenty, and still more slowly 

 to between thirty and forty, when it reaches its maximum. Beyond this period, 

 as age advances and the mental faculties decline, the brain diminishes slowly 

 in weight, about an ounce for each subsequent decennial period. These results 

 apply alike to both sexes. 



The size of the brain appears to bear a general relation to the intellectual 

 capacity of the individual. Cuvier's brain weighed rather more than 64 oz., 

 that of the late Dr. Abercrombie 63 oz., and that of Dupuytren 62^ oz. On 

 the other hand, the brain of an idiot seldom weighs more than 23 oz. 



The human brain is heavier than that of all the lower animals excepting the 

 elephant and whale. The brain of the former weighs from 8 Ib. to 10 Ib. ; 

 and that of the whale, in a specimen seventy-five feet long, weighed rather 

 more than 5 Ib. 



MEDULLA OBLONGATA. 



The Medulla Oblongata is the upper enlarged part of the spinal cord, and 

 extends from the upper border of the atlas to the lower border of the pons^ 

 Varolii. It is directed obliquely downwards and backwards; its anterior sur- 1 

 face rests on the basilar groove of the occipital bone, its posterior surface is 

 received into the fossa between the hemispheres of the cerebellum, forming the 

 floor of the fourth ventricle. It is pyramidal in form, its broad extremity' 

 directed upwards, its lower end being narrow at its point of connection with 

 the cord. It measures an inch and a quarter in length, three-quarters of an 

 inch in breadth at its widest part, and half an inch in thickness. Its surface is 

 marked, in the median line, in front and behind, by an anterior and posterior 

 median fissure, which are continuous with those of the spinal cord. The an- 

 terior fissure contains a fold of pia mater, and terminates just below the pons 

 in a cul-de-sac, the foramen caecum. The posterior is a deep but narrow fissure, 

 continued upwards along the floor of the fourth ventricle, where it is finally 

 lost. These two fissures divide the medulla into two symmetrical halves, each 

 lateral half being subdivided by minor grooves into four columns, which, from 

 before backwards, are named the anterior pyramid, lateral tract and olivary body, 

 the restiform body, the posterior pyramid. 



