THE CEREBRUM, AND ITS FUNCTIONS. 693 



of the healthy brain seems to be about 64 oz., and the minimum about 31 

 oz. But in cases of Idiocy, the amount is sometimes much below this; as 

 low a weight as 20 oz. having been recorded. It appeai-s, from the investi- 

 gations of M. Bourgery, that the relative sizes of the different component 

 elements of the Human Eucephalon are somewhat as follows. Dividing 

 the whole into 204 parts, the weight of the Cerebrum will be represented 

 by about 170 of those parts, that of the Cerebellum by 21, and that of the 

 Medulla Oblongata with the Optic Thalami and Corpora Striata by 13. 

 The weight of the Spinal Cord would be, on the same scale, 7 parts. Hence 

 the Cerebral Hemispheres of Man include an amount of nervous matter, 

 which is four times that of all the rest of the Cranio-Spinal mass, more than 

 eight times that of the Cerebellum, thirteen times that of the Medulla Oblon- 

 gata, etc., and twenty four times that of the Spinal Cord. The absolute weight 

 of the cerebral hemispheres varies according to Meynert from 17,000 to 21,600 

 grains. The average weight of the whole Eucephalon in proportion to 

 that of the body, in man, taking the average of a great number of observa- 

 tions, is about 1 to 36. This is a much larger proportion than that which 

 obtains in most other animals; thus the average of Mammalia is stated by 

 M. Leuret to be 1 to 186, that of Birds 1 to 212, that of Reptiles 1 to 1321, 

 and that of Fishes 1 to 5668. It is interesting to remark, in reference to 

 these estimates, that the Encephalic prolongation of the Medulla Oblongata 

 in Man (being about one-sixteenth of the weight of the whole Encephalou) 

 is alone more than twice as heavy in proportion to his body, as the entire 

 Eucephalon of Reptiles, and ten times as heavy as that of Fish. But there 

 are some animals in which the weight of the Encephalon bears a higher 

 proportion to that of the body than it does in Man ; thus in the Blueheaded 

 Tit, the proportion is as 1 to 12, in the Goldfinch as 1 to 24, and in the Field- 

 mouse as 1 to 31. It does not hence follow, however, that the Cerebrum is 

 larger in proportion; in fact, it is probably not nearly so large; for in Birds 

 and Rodent Mammals, the Sensory Ganglia form a very considerable pro- 

 portion of the entire Encephalon. M. Baillarger has shown that the surface 

 and the bulk of the cerebral hemisphere are so far from bearing any con- 

 stant proportion to each other in different animals, that notwithstanding the 

 depth of the convolutions in the Human Cerebrum, its bulk is 2i times as 

 great in proportion to its surface as it is in the Rabbit, the surface of whose 

 Cerebrum is smooth. The entire surface of the human cerebrum is esti- 

 mated by him at about 670 square inches. The specific gravity of the Brain 

 has been made the subject of careful research by Dr. Bastian, who finds the 

 average of the gray substance to be 1.030, and of the white 1.040. 



561. The Encephalou altogether receives a supply of Blood, the amount 

 of which is very remarkable, when its comparative bulk is considered ; the 

 proportion which goes to it being, according to the estimate of Haller, as 

 much as one-fifth of the whole mass. The manner in which this blood is 

 conveyed to the brain, and the conditions of its distribution, offer some pecu- 

 liarities worthy of notice. The two Vertebral and two Carotid arteries, by 

 which the blood enters the cavity of the cranium, have a more free commu- 

 nication by anastomosis than any similar set of arteries elsewhere ; and this 

 is obviously destined to prevent an obstruction in one trunk from interrupt- 

 ing the supply of blood to the parts through which its branches are chiefly 

 distributed, the cessation of the circulation through the nervous matter 

 being immediately productive of suspension of its functional activity. 1 Not 



1 M. Kobin (Journal de In Physiologic, vol. ii, p. 537) has described an accessory 

 tissue around the capillaries of the brain, in the space between which and the propeV 

 Tunica adventitia, free nuclei, fatty masses, and granules of htematosin, are observa- 

 ble. M. Kobin seems to be of opinion that these are the lymphatics of the brain. 

 See also Strieker in idem, 1867, p. 652. 



