270 



animals, the prodigious'developement of the muscles required nerves of 

 motion of a proportionate size; hence, in them, the cerebral mass, com- 

 pared to the nerves and spinal marrow, is very inconsiderable. It is ob- 

 served, that there exists the same relation, in men of an athletic dispo- 

 sition ; the whole nervous power seems employed in moving their large 

 muscles, and the nerves, though very small in proportion to the rest of 

 the body, are, however, very large, if compared to the cerebral organ. 

 In children, in women, and individuals possessed of much sensibility, the 

 nerves are very large in proportion to the other parts of the body, they 

 decrease in size and shrink in persons advanced in years; the cellular 

 tissue which surrounds them, becomes more consistent, adheres to them 

 more closely; and there exists a certain analogy between the nerves of 

 old men, enveloped by that yellowish tissue, which makes their dissection 

 laborious, and the branches of an old tree covered over by a destructive 

 moss. 



As the uses of the nerves cannot be explained independently of those 

 of the brain, I shall now go on to consider this important viscus. 



CXLI. Of the spinal cord, and its functions*. This part of the nervous 

 system ought no more to be called the spinal prolongation of the ence- 

 phalon, as it has been by some writers, than it ought to be named the 

 spinal marrow: both designations are equally erroneous. It is indepen- 

 dent of the encephalic organ. As the central portion of the nervous 

 system, it is to be found in many animals which possess no brain, and 

 its volume is not proportionate to that of this organ. The ox, horse, and 

 sheep, for example, which have smaller brains than man, have a much 

 larger spinal cord. It is found in acephalous foetuses, where the brain 

 never existed. This latter organ appears to be superadded to it, and that 

 only in the perfect animals, its proportionate size being always in an in- 

 verse ratio to the spinal cord. This part of the nervous system cannot, 

 therefore, be considered as a production from the brain, and as formed 

 by a collection of nerves which successively detach themselves from it. 

 Its volume does not gradually diminish, owing to the nerves which it 

 sends off'; and instead of presenting the characters of a cord which gra- 

 dually decreases in thickness as it advances from the brain, it consists of 

 a set of knots, bulbs, or separate prominences, equal in number to the 

 pairs of nerves which arise from it. Finally, the spinal marrow is formed 

 in the foetus before- either cerebellum or cerebrum; these organs proceed- 

 ing from it, and not it from them. About the second month of the foetal 

 existence, the first epoch at which the brain can be rendered apparent 

 by the action of alcohol, this organ is uncommonly small in proportion 

 to the size of the spinal marrow, and arises evidently from a prolonga- 

 tion of the pyramidal eminences and the corpora oblivaria. The different 

 parts of the encephalic mass are gradually formed by the. successive de- 

 velopement of the corpora pyramidalia, and it is only towards the end of 

 gestation, that the hemispheres are fully formed!- 



The special functions that may be assigned to the spinal cord, are dif- 

 ferent from those performed by the brain. In the spinal marrow resides 

 the source of all the movements, both voluntary and involuntary, that are 

 performed by the animal economy: it presides over those of the heart, of 



* The whole of this section has been translated from the last French edition of this 

 work. Copland. 

 + See APPENDIX, Note D D. 



