pose nearly the whole of the crura cerebri. The interior of these crura, 

 contains a certain quantity of grey substance, which is what nourishes 

 the nervous fibre*. On reaching the ventricles, these peduncles, or rather 

 the two fasciculi which form them, meet with large ganglions, full of 

 grey substance ; these have long been called thalami optici, though they 

 do not give origin to the optic nerves. There the fibres are sensibly en- 

 larged : and they pass from the thalami optici into new ganglions. 

 These are the corpora striata, and the striae which are apparent on cut- 

 ting these pyriform masses of grey substance, are only the same fibres, 

 which, enlarged, multiplied, and radiated, spread out in the manner of 

 a fan, towards the lobes of the brain, where, after forming by their ex- 

 pansion, a whitish and fibrous substance, they terminate at the outer 

 part of that viscus, forming its convolutions, all covered with the sub- 

 stance in which are terminated, in like manner, the extremities of the 

 diverging fibres. From this grey substance, proceed converging fibres 

 tending from all parts of the periphery to the centre of the brain, where 

 they unite to form the different commissures, the corpus callosum, and 

 other productions, destined to facilitate the communication of the two 

 hemispheres!. 



The exterior of the brain may, therefore, be considered as a vast ner- 

 vous membrane, formed by the grey substance. To form a clue concep- 

 tion of its extent, it must be understood, that the convolutions of the 

 brain, are a sort of duplicatures, susceptible of extension by the unfold- 

 ing of two contiguous medullary lamina, which form its base. The exte- 

 rior surface of the brain, by means of this unfolding, offers them some 

 relation to the skin, a vast nervous expanse every where covered by a 

 sort of pulpy substance, known by the name of the rete mucosum of 

 Malphigi. M. Gall compares this cutaneous pulp, to the cineritious sub- 

 stance which forms the outer part of the brain, and, I must confess, it is 

 not every one that will admit the analogy. However, true it is, that the 

 brain consists, principally, of a mass of ganglions, that it produces nei- 

 ther the elongated medulla, nor the spinal marrow, that this last may be 

 considered as a series of ganglions, united together that the vertebral nerves 

 arise from the greyish pulp of which the spinal marrow is full, as is best 

 seen in animals without a brain, but not the less provided with a spinal 

 marrow, or series of ganglions, from which the nerves arise. The gan- 

 glions, or rather the grey substance which they always show, produce 

 the nervous fibres, and thicken the nervous cords that pass through 

 them. 



That is the only use that can be assigned to these parts of the nervous 

 system ; for, if they were meant to withdraw from the dominion of the 

 will, the parts in which they are found, why do not the ganglions of the 

 vertebral nerves fulfil the same function ? All these nerves communicate 

 by the reciprocal anastamoses. These communications, in man, are 

 equivalent to a real continuity. In truth, the brain acts upon the nerves 

 that proceed from the spinal marrow, is if this were one of its produc- 

 4|ns, and all the nervous fibres, spread through the different organs, had 

 an extremity terminating in this viscus. 



* This means simply that the cineritious substance is found where the fibrous matter 

 is increased, or ganglia are formed. As to its nourishing the fibrous structure, it is a 

 mere assumption, or begging the question.-*- Godman. 



f See APPENDIX, Note D D. ^ 



