18 THE BRAIN AND NERVES AS [i. 



from the vessels of the gray matter of the brain into the hollow 

 tubes of the medullary matter, which is carried in the tubes 

 of the nerves to their termination, and supplies the principle 

 whereby the nerves are rendered capable of being the organs of 

 the senses and of movements/^ (Haller's ^Physiology/ sect. 383.) 

 As the gray or cortical substance of the brain is the secreting 

 organ of the vital spirits, the medullary substance must be the 

 seat of the animal-sentient forces. The secretion and action 

 of the vital spirits will be considered afterwards (374). 



12. The brain also gives origin to all the nerves, which are 

 continuations of the cortical substance, given off partly from 

 it directly in small bundles, termed the cranial nerves, and 

 partly from a thick cord of it, termed the spinal marrow, which 

 passes downwards through the spine, whence the nerves are 

 distributed to all parts of the body. 



13. The nerves generally are enclosed in an investing mem- 

 brane, and, like the blood-vessels, divide and subdivide in the 

 greater part of the body, which they either penetrate or form 

 loops in ; or, having lost their investing membrane, are so incor- 

 porated with the soft parts, that they can be no longer traced. 

 Their essential element is the medullary matter of the brain, 

 or the soft substance enclosed within the cortical substance; 

 whereas their investing membrane seems to have no share in 

 the proper animal functions allotted to them. Every nerve is 

 a bundle of much smaller fibrils, each of which rims an inde- 

 pendent course to and from the brain. Every nerve has its 

 special point of origin in the brain, and every fibril must have 

 its special origin from that point, from whence it takes an 

 entirely independent and separate course through the medulla 

 oblongata and the spinal cord, to its minutest termination. 

 According to all probability, the fibrils of the nerves are hollow 

 canals. 



Since these propositions are of very great importance in 

 the present work, and much will be deduced from them, it isj 

 proper to state that they are taken from the Physiology of j 

 Haller, the greatest anatomist and physiologist of the day. 



14. The nerves so terminate externally, that either they are) 

 incorporated with other machines of the organism appropriated; 

 to certain movements; or they are distributed over the skin or ■ 

 other parts of the body, as the eyes, ears, &c., without exciting 



