NERVOUS CENTRES. (HUMAN ANATOMY. THE ENCEPHALON.) 



661 



merit of physiology, that a distinct series of 

 nervous fibres is directed to each class of 

 actions, those, namely, of sensation and volition, 

 and those which are independent of the brain. 

 Mr. Grainger was the first who offered a distinct 

 solution to the anatomical problem which arose 

 out of this hypothesis. Probable as his expla- 

 nation appears to be, a candid review of the 

 observations which have been hitherto made 

 obliges me to state my opinion that the question 

 is still subjudice, and that further research is 

 necessary to prove unequivocally that of the 

 fibres composing the roots of the nerves, some 

 pass upwards and enter the brain, and others 

 do not pass beyond the grey matter of the 

 spinal cord. And this inquiry demands more 

 than ordinary care, for the mind of an observer 

 would be easily biased by so attractive an hy- 

 pothesis as that above referred to. 



It is not from physiological experiment nor 

 from coarse dissections that we can expect a 



solution of this difficult but most important 

 problem. We must look to the microscopical 

 analysis of the anatomical elements of the 

 spina! cord, as well as of the encephalon, for 

 the most exact results upon all questions con- 

 nected with the working of these centres. In 

 a subsequent part of the article I shall give an 

 account of the present state of our knowledge 

 of this most interesting subject, having first 

 examined the coarser anatomy of the several 

 parts of the encephalon. 



2. OF THE ENCEPHALON. Gr. {yxsipaXoK or 

 fyxe^aAo; (tit T xsposAi,); Fr. I' Encephale, le 

 cerveau; Germ, das Gehirn ; The Bruin. This 

 term is used here in its strictly etymological 

 sense to denote that part of the cerebro-spinal 

 centre which is contained within the cavity of 

 the cranium. Although it forms a great mass, 

 continuous throughout, it offers certain very 

 obvious subdivisions, which may be more con- 

 veniently described separately (fig. 379). Be- 



a 



This figure displays well the subdivision of 

 the encephalon adopted in this article. 

 ( After Mayo.) 



1. Medulla oblongata. 



p, anterior pyramids. 

 o, olivary bodies. 

 r, restiform bodies. 



2. Mesocephale 



y, pons Varolii. 



c, corpora quadrigemina. 

 3. Cerebellum. 

 4. Cerebrum 



a, anterior lobe. 

 m, middle lobe. 



f, fissura Sylvii. 



b, posterior lobe. 



fore proceeding, however, to the description of keeps pace with that of the body. In com- 



these portions, it will be necessary to take a paring that of the four classes of vertebrate 



brief review of some general points connected animals, we observe a manifest increase of its 



with the entire encephalic mass. size as compared with the body in the follow- 



The size of the encephalon by no means ing order, fishes (minimum), reptiles, birds, 



