■2:\ 



AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



showing in some measure the relative physiological importance of the several 

 parts. 



Weight of the Encephalon and Spinal Cord. — When the weight of any 

 portion of the aervous system is taken, the final record represents, in addi- 

 tion to the weight of the nerve-tissues proper, that of the supporting and 

 nutritive tissues normally associated with them, together with the enclosed 

 blood and lymph. It is, however, assumed that under normal conditions the 

 relation between the nervous and non-nervous tissues is nearly a constant one, 

 and that the results of different weighings are therefore comparable among 

 themselves. 



Outside of the nervous tissue proper are the pia and the fluid contained in 

 the vessels and ventricular cavities. Sometimes the encephalon is freed from 



Til.. 117. — Showing tin- principal divisions of the encephalon made for the study of its weight: 1, 

 hemisphere seen from the side, fissuration according to Eberstaller ; 2, mid-brain, region of the quad- 

 rigemina ; 3, pons; 1, cerebellum, or hind-brain ; 5, bulb, or after-brain. Divisions 2, 3, and •'>. taken 

 r, form what is designated the "stem " in the tables of Boyd (modified from Quain's Anatomy). 



the pia and fluid, and at others they are weighed all together. According to 

 Broca, 1 the weight of the pia covering the encephalon is, in normal males, as 

 follows : 



20 to 30 years ' 45 gms. 



31 to 40 " 50 " 



60 " 60 " 



The cast of the ventricles as made by Welcker displaces 26 c.c. of water, 

 which gives an idea of the normal capacity of these cavities. In man, the 

 gray matter of the cerebrum has, on the average, Si per cent, of water; while 

 the white matter from various parts of the central system has 70 per cent. 2 



1 Broca, quoted by Topinard: Elements <F ArUhropologie generate, 1885. 



2 Halliburton : Journal of Physiology, 1894. 



