EXPLANATIOX OF THE PLATES. 4G5 



ascribed to the human embryo and to some animals in Quain (A, II, 543) is due to the 

 artificial rupture of the natural connections ; see p. 53fi of the same work. 



Attention is called to the following points, chiefly in comparison with the human 

 brain : — 



The appearance of tlie Rx. mesalis {Rx. ma.) on the meson, and tlie presence of two 

 shallow fissures, postradicalis and praeradicalis {FF. prd. and prrd.) between it and the 

 adjoining surfaces of the hemisphere. 



The large size of the commissures, especially the medicommissura, which nearly fills 

 the dorsal part of the diacoelia {dc). 



The non-appearance of the porta when the mieson is viewed squarely ; it is doubtful 

 whether the human " foramen of Monro " is really visible from the meson. 



The less extent of the callosum, especially of its rostrum (rm.). In some human 

 brains the rostrum does not extend so far as is usually represented. 



The darker spot on the section of the hypophysis represents the space occupied by the 

 ental mass, which has been removed. 



The relations of the pia are not indicated at all, and are not well understood, especially 

 between the cerebellum and the metencephalon and mesencephalon. 



PLATE III. 



With the exception of Fig. 13, all the figures upon this plate represent the natural 

 surfaces of regions which are more or less completely concealed by other parts in the 

 undissected brain. 



§ 1163. Fig. 5. — The cephalic aspect of the prosencephalon. From Prep. 

 294; x2. 



The hardened brain was transected at the F. postica, so that the preparation includes 

 only the cephalic two thirds of the prosencephalon. 



The drawing represents the preparation tilted up so as to expose the ventral aspect 

 foreshortened. 



As compared with Fig. 6, this might well have been made of the natural size. A less 

 regularly symmetrical brain would have been more instructive. One of the Crura olfac- 

 toria should have been divided at a little greater distance from the prosencephalon. 



So far as appears in the figure, the fissures are remarkably alike upon the two sides ; 

 the left F. ansata {F. an.), however, only the meso-cephalic end of which appears in the 

 figure, presents the somewhat unusual but very sugp^estive condition of entire independ- 

 ence of the lateralis (which is invisible) and the coronalis {F. cor.). On the right side it 

 is joined by the former fissure. 



The right F. Sylviana (F. 8.) is shorter than the left, and presents a slight terminal 

 bifurcation which is not shown. 



In consequence of the removal of the Ldbi olfactorii and the tilting of the whole prepa- 

 ration, so much of the F. rhinalis (F. rh.) as lies cephalad of its union with the super- 

 orbitalis {F. so.) is practically obliterated, and the remainder of it is so foreshortened as to 

 appear as an insignificant intermediate portion of an extensive u-shaped fissure formed by 

 the FF. Sylviana (F. 8.) and superorbitalis {F. so.). "The appearances thus presented 

 are suggestive in view of the idea of Meynert ( /, 12), which I also entertained at one time 

 (11,225), that the F. superorbitalis represents the 'anterior branch' of the human 

 F. Sylviana, and that the intervening region corresponds to the ' operculum.' " 



A slight preponderance of the left hemisphere just caudad of the F. Sylviana is some- 

 30 



