NERVES OF MAMMALIA. 167 



Believing that he could f trace down the crura of the cerebrum 



O 



into the anterior fasciculus of the spinal marrow, and the crura 

 of the cerebellum into the posterior fasciculus, I thought/ he 

 writes, p. 21, ( that here I might have an opportunity of touch- 

 ing the cerebellum, as it were, through the posterior portion of the 

 spinal marrow, and the cerebrum by the anterior portion. To this 

 end I made experiments which, though they were not conclusive, 

 encouraged me in the view I had taken.' 



' I found that injury done to the anterior portion of the spinal 

 marrow convulsed the animal more certainly than injury done to 

 the posterior portion, but found it difficult to make the experi- 

 ment without injuring both portions.' 



( Kext considering that the spinal nerves have a double root, 

 and being of opinion that the properties of the nerves are derived 

 from their connections with the parts of the brain, I thought that 

 I had an opportunity of putting my opinion to the test of experi- 

 ment, and of proving at the same time that nerves of different 

 endowments were in the same cord, and held together by the same 

 sheath. 



' On laying bare the roots of the spinal nerves, I found that I 

 could cut across the posterior fasciculus of nerves, which took its 

 origin from the posterior portion of the spinal marrow, without 

 convulsing the muscles of the back ; but that on touching the 

 anterior fasciculus with the point of the knife, the muscles of the 

 back were immediately convulsed' (ib. p. 22). 



The ventral as well as the dorsal roots of the spinal nerves are 

 traceable to the contiguous parts of the grey tract, the latter more 

 immediately, as at k, fig. 40. They are severally connected with, 

 but do not constitute, the white columns from which they emerge. 

 Comparative anatomy testifies plainly against the anterior and 

 posterior columns being aggregates and brainward continuations 

 of the motory and sensory roots. Thus, in the instance of such 

 unusual elongating growth of the myelon as takes place in the 

 neck of the foetus of the Giraffe, as many of the roots of a nerve, 

 the origin of which may be so extended by interstitial myelonal 

 increase, incline tailward as head ward (p. 75). And accurate 

 experiment gives the same response, sensation continuing or 

 being heightened in parts supplied by nerves beyond the place 

 of the myelon of which the dorsal or posterior columns have been 

 divided. 



The most constant anatomical concurrence with sensory func- 

 tion is the ganglion, fig. 136, G, fig. 131, 9. 



In all Mammals the trunk, fig. 136, C, formed by the union of 

 the two roots soon divides into an anterior and a posterior pri- 



