204 



ANATOMY FOR, NURSES. [CHAP. XVIII. 



the brain; it also forms sheaths for the nerves passing out of the 



skull. It ma}' be called the protective membrane. 



The pia mater is a delicate membrane of connective tissue, 



containing an exceedingly abundant network of blood and 

 lymph vessels. It dips down into all the 

 crevices and depressions of the brain, 

 carrying the blood-vessels which go to 

 every part. It may be called the vascular 

 or nutritive membrane. 



The arachnoid is a delicate membrane 

 which is placed outside the pia mater. It 

 passes over the various eminences arid de- 

 pressions on the surface of the brain, and 

 does not dip down into them like the pia 

 mater. Beneath it, between it and the 

 pia mater, is space (sub-arachnoid space) 

 in which is a certain amount of fluid. The 

 sub-arachnoid space at the base of the brain 

 is of considerable size, and contains a large 

 amount of this clear limpid fluid, called the 

 cerebro-spinal fluid. This fluid probably 

 acts as a sort of protective water-cushion to 

 the delicate nervous structure, and pre- 

 vents the effects of concussions communi- 

 cated from without. 



The brain is a semi-soft mass of white 

 and gray matter. The white matter con- 

 sists of very small, medullated nerve-fibres, 

 running in various directions, and sup- 

 ported by a delicate connective tissue 

 FIG. 119. SIDE VIEW framework. The gray matter consists of 



OF THE BRAIN AND SPI- ce u s an( j fi ne Rray fibres, also supported 



NAL CORD IN PLACE. The . 



parts which cover the cere- by Connective tissue. 



bro-spinal centre are re- The bmin ig divided into four principal 



moved. * - 1 - 



parts: the cerebrum, the cerebellum, the 

 pons Varolii, and the medulla oblongata. 



The medulla oblongata is a continuation of the spinal cord, 

 which, on passing into the cranial cavity through the foramen 

 magnum, widens into an oblong-shaped mass. It is directed 

 backwards and downwards, its anterior surface resting on a 



