136 HUMAN PHYSIOLOGY. 



to fall on one side and roll rapidly on its longitudinal axis. According to 

 Schiff, if the peduncle be divided from behind, the animal falls on the same 

 side as the injury; if the section be made \r\front, the animal turns to the 

 opposite side." 



Disease of the cerebellum partially corroborates the result of -experi- 

 ments ; in many cases symptoms of unsteadiness of gait, from a want of 

 coordination, have been noticed. 



Comparative anatomy reveals a remarkable correspondence between the 

 development of the cerebellum and the complexity of muscular actions. It 

 attains a much greater development, relatively to the rest of the brain, in 

 those animals whose movements are very complex and varied in character, 

 such as the kangaroo, shark and swallow. 



The cerebellum may possibly exert some influence over the sexual func- 

 tion, but physiological and pathological facts are opposed to the idea of its 

 being the seat of the sexual instinct. It appears to be simply a centre for 

 the coordination and equilibration of muscular movements. 



CEREBRUM. 



The Cerebrum is the largest portion of the encephalic mass, constituting 

 about four-fifths of its weight ; the average weight in the adult male is from 

 48 to 50 ozs., or about three pounds, while in the adult female it is about 

 five ozs. less. After the age of forty the weight of the cerebrum gradually 

 diminishes at the rate of one ounce every ten years. In idiots the brain 

 weight is often below the normal, at times not amounting to more than 

 twenty ounces. 



The Blood Supply to the cerebrum is unusually large, considering its 

 comparative bulk ; nearly one-fifth of the entire volume of blood being dis- 

 tributed to it by the carotid and vertebral arteries. These vessels anastomose 

 so freely, and are so arranged within the cavity of the cranium, that an 

 obstruction in one vessel will not interfere with the regular supply of blood 

 to the parts to which its branches are distributed. A diminished amount, or 

 complete cessation, of the supply of blood is at once followed by a sus- 

 pension of its functional activity. 



The cerebrum is connected with the pons Varolii and medulla oblongata 

 through the crura cerebri, and with the cerebellum, through the superior 

 peduncles. It is divided into two lateral halves, or hemispheres, by the 

 longitudinal fissure running from before backward in the median line ; each 

 hemisphere is composed of both white and gray matter, the former being 



