CH. III.] THE BRAIN. 83 



the nerves along which conceptional or internal impressions are 

 transmitted from the brain. 



155. To understand this matter rightly^ the meaning of the 

 term mechanical machines used in this whole treatise, must 

 be properly comprehended ; it must be understood to include 

 all the organs of the body, except the brain and nerves, which 

 are proper animal machines. Consequently muscles, tendons, 

 membranes, vessels, glands, bones, cartilages, viscera, &c., are all 

 mechanical machines. Although many of these are endowed 

 with animal moving forces, they are so endowed, only through, 

 and in virtue of, the nerves with which they are supplied. So 

 also the organs of the external senses, although endowed with 

 sensitive nerves, are only mechanical machines, and even the 

 brain and nerves contain the latter. 



156. There are no other mechanical machines in direct con- 

 nection with the brain, than certain glands, the meninges, and 

 the circulating and lymphatic vessels. Consequently, these are 

 the only machines, in which material ideas can develope sentient 

 actions directly in the brain itself, without the aid of the nerves. 



157. The uses of the glands situate on the membranes of the 

 brain, and in close proximity to it, are altogether unknown ; but 

 they probably constitute a part of its mechanical structure. 



158. The membranes enclosing the brain, and partly the 

 nerves, belong to the same class (the mechanical) as tendons, 

 ligaments, &c. They are not only insensible, but the brain 

 itself seems to have no influence on them, except in commu- 

 nicating the mechanical movement (24) which it possesses itself. 



159. The tubes, and especially the vascular system, remain 

 only to be noticed among the mechanical machines which are 

 in connection with the brain, and in these, material ideas can 

 develope true sentient actions. The cortical substance is almost 

 wholly a tissue of tubes ; it is not the organ of the conceptive 

 faculty, nor the seat of the animal-sentient forces, but the 

 organ for secreting the vital spirits, which it supplies to the 

 medulla of the brain, and thence to the entire system of animal 

 machines (the nervous system) (11) ; in this respect it can be 

 considered as a viscus of the head, whose proper function is the 

 secretion of certain fluids from the blood; which fluids con- 

 stitute, however, an essential part of the animal machines (9) ; 

 it is, therefore, really a mechanical machine (155), but in virtue 



