from its substance. Their volume has no relations to its bulk,,%ut are 

 proportionate to the perfection of the different senses, in the various spe- 

 cies of animals; thus, the olfactory nerve, which is very large in the mole, 

 is small in the eagle, while the optic nerve is on the contrary largely de- 

 veloped in the latter. 



The spinal marrow may be considered as a series of ganglions., com- 

 municating with each other and with the brain*. These ganglions are 

 of a size proportionate to that of the nerves which originate from them. 

 It is owing to this that the spinal marrow is thicker towards the inferior 

 part of the cervical and dorsal regions, than in other portions of its 

 length. Can, therefore, the vertebral column be compared to a Galva- 

 nic pile, of which the spinal cord is the conductor, of which the brain 

 and the parts of generation form the two extremities^ and constitute, in 

 a manner, the two poles of this kind of electro-motive apparatus ? Ob- 

 servation establishes, it may be said, a sort of antagonism between these 

 two organs. Is there any analogous opposition existing between the ce- 

 rebral nervous system and that which forms the grand sympathetic 

 nerves? We have formerly remarked more than once, how ill founded 

 this attempt at identifying the vital phenomena with those of electricity, 

 appears to us. 



The commnuication of the spinal marrow with the brain is established 

 by the medium of a double bundle of fibres which, crossing each other, 

 form the copora pyramidalia, and direct themselves towards the brain, 

 where we shall find them again when the structure of this viscus comes 

 under consideration. 



CXLII. Of the coverings of the brain. If it be true, that one may judge 

 of the importance of an organ, by the care which nature has taken to 

 protect it from external injury, no organ wi^l appear of greater impor- 

 tance than the brain, for, no one app : e1?P9Ho have been protected with 

 greater care. The substance of this viscus has so little consistence, that 

 the slightest injury would have altered its structure, and deranged its 

 action ; hence it is powerfully guarded by several envelopes, the most 

 solid of which, is the bony case, in which it is contained. 



No part of anatomy is better understood, than that of the many bones 

 which, by their union, form the different parts of the human head. 

 Every thing that relates to the place they occupy, to their respective 

 size, to their projections and depressions to the cavities*whose parietes 

 they form, every thing that relates to their internal structure, to the dif- 

 ferent proportions of their component parts, to the aggregation of some 

 of these substances, in certain points of their extent, has been described 

 by several modern anatomists, with an accuracy which it would not be 

 easy to surpass. Several, however, have not sufficiently appreciated the 

 direct influence of their mode of union on the purposes which they are 

 destined to fulfil ; no one has insisted sufficiently on the manner in which 

 they all concur to a principle object ; the preservation of the organs en- 

 closed within the skull. 



Hunauld, in a memoir inserted among those of the Academy of Sciences, 

 for the year 1730, was the first that endeavoured to account for the ar- 

 rangement of the articulating surfaces of the bones of the skull. After 

 laying down a few principles on the theory of arches, and after showing, 



See APPENDIX, Note D D. 



