FIG. 179 A. Central or- 

 gans of the nervous sys- 

 tem. F. T. O., frontal, 

 temporal and occipital 

 lobes of the cerebrum; C, 

 cerebellum; P, pons varo- 

 lii; mo, medulla oblon- 

 gata; ms-ms, upper and 

 lower limits of the spinal 

 cord; CVIII, 8th cervi- 

 cal nerve; DXII, 12th 

 dorsal nerve. (Qua in 

 after Bourgery.) 



THE ANIMALS AND MAN 



cavities of the vertebrae. Both brain 

 and spinal cord are further protected 

 by three membranes of connective tis- 

 sue. Of these the dura mater is the 

 tough outer coat. The pia mater is 

 the delicate inner membrane. This 

 is closely applied to the surface of 

 the brain and spinal cord following 

 all the fissures. It is vascular, that is, 

 it contains the blood-vessels which 

 supply the cells of nervous tissue with 

 blood and oxygen and remove waste. 

 Between the dura mater and the pia 

 mater is an inner coat, the arachnoid 

 membrane. This membrane contains 

 large spaces filled with a fluid (the 

 cerebro-spinal fluid). This, like the 

 serous fluids surrounding the heart and 

 lungs, is a protective fluid. 



Structure of the brain (fig. 179 A 

 and fig. 179 B). Like the brain of the 

 cat (see page 67) the human brain 

 consists primarily of three parts, the 

 fore brain, mid brain, and kind brain. 

 The fore brain or cerebrum is large and 

 conspicuous. It comprises nine-tenths 

 of the brain's bulk and almost 

 completely covers the other parts. 

 This disproportion in size gives some 

 indication of its very great importance 

 as compared with that of the other 

 parts. The cerebrum is characterized 

 by many convolutions. Seen from 

 above its right and left halves (hemi- 

 spheres) are separated from each other 



