Wilder.] ^^^ [July 15, 



3. The natural endymal surfaces of tlie trneficelue or "ventricles." Of 

 course the "lateral ventricles," procoelise, do not appear. 



4. The cut surfaces of the commissures and other parts which cross the 

 meson, or lie upon it. In the cerebellum {cbl. ) the relative areas of the ental 

 alba and the ectal cinerea forming the arbor vitoe, {arb. ), are indicated by the 

 shading ; with less definiteness, the alba is shown in the callosum [cl.), the 



fornix if.), the prwcommissura (prcs.), the postcommissura {pes.), the co)n- 

 missura habenarum {cs. 7i.), and the chiasma {ch.). The section of the 

 medifiommissura (mes.) should appear as if composed, at least chiefly, of 

 cinerea, but no attempt has been made to indicate the nature of the cut sur- 

 faces of the Crista fornicis {Grs.f.), the terma (t.), the hypophysis (Jiph.), 

 the infundibulwn (inf.), the basicommissura (bcs.), the conarium (en.), the 

 opt'ici and postojJtici (02). and pop.), the vahula («».), the Crura cerebri (Gr. 

 cb ), the metatela (mttl.), or the rest of the epencephalon- and meten- 

 cephalon (mten.). The extent of the transverse fibres of the pons (pn.) 

 should have been represented, at least approximately. 



So much of the cephalic boundary of the aula (A.) as intervenes be- 

 tween the prcecommissura (prcs.) and the crista (Crs. f.) is very thin, and 

 is too indistinctly shown in the figure. Neither here nor at any other point 

 is there any such interruption of the wall as would form a communication 

 between the true coelise and the pseudocoelia or the ectal surface of the brain. 

 It is probable that the presence of such a communication as is ascribed to 

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

 the artificial rupture of the natural connections. 



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

 the human brain : — 



The appearance of the Bx. mesalis (Rx. ms.) on the meson, and the 

 presence of two shallow fissures, postradicalis and pixeradicalis (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 diaccelia (dc). 



The non-appearance of the porta when the meson 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 under- 

 stood, 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 conceal- 

 ed by other parts in the undissected brain. 



