r,:-j ////: t i:\ i /,M/. .1 A 7s "/' v///: M:I;\<H > > >> / I:M. 



the cells of the grey substance, or reach the em-cphalon by remaining in tin; 

 corresponding moiety of the medulla; for instance, tin; fibres of the right 

 hiilf of tin- medulla gain the brain without passing into the lel't h:ilf. 

 Those of the lateral cords decussate, each cord Bending to, and receiving 

 from, the other, tubes which cross in the white commissures. The post' riur 

 cords contain fibres that extend directly to tins brain: tin M ai sensorial ; 

 there are also found transverse fibres that enter the cells of the SUJK rim- 

 grey cornua, and others that jass into the cells of the inferior or motor 

 cornua. 



Such is, in a few words, the disposition of the nerve-elements in the 

 medulla. The subject is a very long and complicated one, which cannot 

 be dealt with in a more detailed manner in a work on descriptive anatomy. 



Vessels. The medulla receives arteries from the ramifications of the 

 pia mater. The grey is richer in vessels than the white substance ; the 

 latter is penetrated everywhere by a largo number of minute arteries ; while 

 the first is traversed by the divisions of an artery that is thrown off by the 

 median spinal, and ascends towards the bottom of the inferior fissure. The 

 veins follow the arteries, and constitute two somewhat voluminous vessels 

 that pass along the grey commissure, to the right and left of the central 

 canal. 



DIFFERENTIAL CIIABACTKBS IN THE SPINAL CORD OF OTHER TUAN SOUPED ANIMALS. 



In all the species, the white and grey substances nft'eet the disposition ;il>\<- de- 

 scribed; only fume slight differences in the reciprocal volume of < arh h;i\. 

 remarked. As in the Horse, the spinal medulla docs not extend Ix-yoiul tin 1 

 region; its length has no relation to that of the coccygeal regiou, as certain ana'omists 

 would, in principle, establish; in the rabbit, for example, the tail of which is very 

 .-I ort, the spinal cord is prolonged into the coccygeal vertebra). 



COMPARISON OF THE SPINAL CORD OF MAN WITH THAT OF ANIMAI.S. 



The spinal m< dulla of the a<lult Mini docs not reach beyond the first lumbar vertebra, 

 though in the fictus it is in the coccyx. It is rounder than in the Horse, and the grey 

 .-nbstance is, relative to the white, more abundant than in the spinal cord of the. di'ine- 

 ticiited animals. The posterior grey cornua arc also larger and less elongated thnn the 

 superior cornua in the Horse ; and the roots of the nerves arc also more voluminous. 



CHAPTEE III. 



THE ENCEPHALOX. 



ARTICLE I. THE ENCEPHALON AS A WHOLE. 



THE eneqriba&M is that portion of the nervous system which is lodged in 

 the cranial cavity. It succeeds, without any line of demarcation, the spinal 

 cord, of which it may bo considered, with regard to its figure, as a kind of 

 efflorescence. 



General form and constitution. In shape it is an ovoid mass, elongated 

 from before to behind, and very slightly depressed from above to below. 



When it is viewed on its superior face (Fig. 821), wo first sec, behind, a 

 white pedicle, the prolongation of the spinal cord, and a single lobe of a 

 grey colour designated the 1-n-i'ln-lliiiii. In front of this is remarked two 

 other lobes, separated from the first by a deep transverse fissure, into which 



