METHODS OP STUnriNO TUM BRAIN. 401 



able functions. Finally, the human brain is usually presented, or 

 at least employed as a standard for comparison. 



From personal experience and from the uniform testimony of 

 our students, we have been led to the following conclusions :— 



(A) The arrangements of the solid parts of the brain are more 

 readily perceived and more easily remembered after the relations 

 of the cavities are fully understood. 



(B) An adequate idea of the circumscription of the cavities in- 

 volves a distinct recognition of their lining and of the investment of 

 the whole brain. 



(C) The general plan of the organ is most readily appreciated if 

 we disregard altogether its organic composition and its direct sub- 

 servience to mental operations, and view it primarily as we might 

 any artificial structure, like a house or a piece of furniture of homo- 

 geneous material. 



(D) Even if, as is commonly the case, the human brain is the 

 ultimate object of inquiry, the brain of some Amphibian should be 

 examined first. 



§ 1052. So far as we know, tlie first three of these propositions have not been distinctly 

 enunciated heretofore. 



The advantage of studying first the cavities of the brain seems to arise from the fact 

 that while the walls are subject to great modificatidBs as to form, thickness, histological 

 composition and connections, the cavities can present differences of only size, shape and 

 degree of circumscription ; their connections are invariable, and of course no structure is 

 predicable of them. Hence fewer considerations are presented to the mind, a matter of no 

 small importance to the beginner. 



§ 1053. To the physiologist the membranous envelopes are of interest only as con- 

 cerned in the vascular supply of the proper nervous tissue, and for most anatomical 

 purposes they are better removed. With them, however, are apt to come away some 

 atrophied parts of the parietes together with the lining of the cavities, so as to leave the 

 latter open at certain points. Hence many figures and descriptions indicate or imply that 

 there are free communications between the cavities and the outside of the brain. 



With poisibly a single exception (§ 1083), this is not the case, in adults at least, and 

 indeed the existence of such communications would be oat of keeping with what is known 

 of the mode of development of the organ. Hence any clear and adequate conception of 

 the relations of the cavities involves the distinct recognition of the presence of the mem- 

 branes and of their general arrangement. 



§ 1054. As to the third proposition, the comparative anatomist and the systematic 

 zoologist especially desire the identification of the various regions of the brain, and the 

 determination of suitable names and terms for description, Even where the histology 

 and functions of the organ are the ultimate objects of its study, the student must first 

 become familiar with the order of succession of the parts, their constant topographical 

 relations and the connections of their cavities, and with the names of them all. 



Now this may be done not only as well, but in our opinion more easily, if all other 

 26 



