228 



TITE REASON WHY. 



- A sound heart L the life of the flesh : but envy is the rottenness of the 

 bones." PROVERBS xiv. 



Fig. 59. SHOWING THE 

 DISTRIBUTION OP NERVES 

 AND VEINS, AND ILLUS- 

 TRATING THE MANNER 

 IN "WHICH THEY PASS 

 THROUGH THE FLESH TO 

 BEACH THE PARTS TO 

 WHICH THEIE FUNCTIONS 

 BELONG. 



954. How can branches proceed 

 from it, if it is so securely encased 

 in bone ? 



Because in the bones, on each side of 

 of the spinal cord, there are smaller 

 grooves for the transmission of the 

 nervous branches. 



955. Of what does the nervous sys- 

 tem consist ? 



Of the brain, the spinal cord, and the 

 branches which are called nerves. 



A B. Veins of the fore-arm. 



B. C;mal formed in the muscle, through which 

 a trunk-vein emerges. 



0. Canal formed in the muscle, through which 

 a large nerve emerges. 



D. Canal through which a vein enters to 

 communicate with the deep muscles of the 

 arm. 



956. What is the constitution of a 

 nerve ? 



It consists of a thin membrane, or sheath, surrounding a greyish 

 oily matter, which forms the nervous marrow. In the centre of 

 this marrow is usually found a small fibre, which is supposed to be 

 the essential part of the nerve ; and most nerves consist of a number 

 of these sheaths enclosing fibres running in parallel directions. 



957. What is the nervous fluid ? 



The term nervous fluid is used to express our ideas of the mode 

 by which the brain and spinal cord influence the remote parts : just 

 as we say the electric fluid, without knowing that such a fluid 

 exists. It is the most convenient form of expression. 



958. How many classes of nerves are there T 



There are : 



1. The nerves of motion. 



2. The nerves of sensation. 



