32 



contiguous to each other, (supposed to secern the 

 animal spirits) which are of themselves oval, but by 

 their mutual pressure become angular, and run wav- 

 ing with each other. 



The inner part (called the medulla) is white, and 

 terminates in another medullary substance, very white 

 and hard, called the corpus callosum. The medulla 

 is thought to consist of fine tubes, which when col- 

 lected into little bundles, and covered with membranes 

 arc termed nerves. 



20. To trace this a little farther. From every 

 point of the outer brain arise minute fibres, which in 

 their progress uniting together, are easily perceptible. 

 These constitute the substance of the inner brain, and 

 of the spinal marrow. In their farther progress they 

 are distinguished by coats 5 detached from the two mem. 

 branes of the brain, into several bundles called nerves, 

 resembling so many horse-tails, each wrapt up in a 

 double tunic. 



Several of these part from the rest in the brain 

 itself, of which there are ten pair ; one on each side. 

 From the spinal marrow there arise thirty pair more* 

 All these, while within the skull or the spme, are 

 pulpous ; but afterwards harden, acquire a coat, and 

 spread through the smallest points of the solid parts 

 of the body. Their coats are every where furnished 

 with blood-vessels, lymphatics^ and vesicle ~f a * 

 Tfiiy tight texture. whi* y ervc to collect, strengthen, 

 and contract their fibres. And if we consider, 1. 

 The great bulk of the brain, cerebellum and spinal 

 marrow, (whereof the whole substance goes to con. 

 stitute nerves, being continued into, and ending iji 

 them :) The great number of nerves distributed 

 hence throughout the whole body : 3. That the brain 

 and spinal marrow are the basis of an embryo, 

 whence the other parts are afterwards formed : And 

 lastly, that there is scarce any part of the body, 

 which does not feel or move ; it may seem not alto- 

 gether improbable, that all the solid parts of the body ? 



