EXPLANATION OF TBE PLATES. 467 



torn from this preparation, and the line of its attacliment is not distinctly shown. Some- 

 thing of its position may be judged from Fig. 7. The caudal orifice of the mesocoelia 

 {msc.) is shown here as a nearly regular circular spot ; iu reality, it presents a slight mesal 

 extension at both the dorsal and ventral sides. Indeed, when carefully examined, the so 

 called " aquseductus Sylvii " is far from being a perfectly simple and uniform tube : its 

 form in man is indicated in Reichert's Fig. 31 (A, Taf. 4). Among the lower mammals it 

 is usually larger, and with the lower vertebrates it often has the proportions of a true 

 ccelia, with lateral extensions. 



The cimbia {cmh.) is partly seen on the right. The geniculata {pgn. a.nd prgn.) do not 

 project as far as they should. The optici are wholly hidden from view by the prominent 

 postoptici (pop.). 



§ 1167. Fig. 9. — The sinistral aspect of the mesencephalon and diencephalon. 

 Prom Prep's 491 and 506 ; x 3. 



The only cut surface shown in this figure is that caused by the oblique transection 

 between the diencephalon and the prosencephalon ; the plane of section followed the 

 cephalic border of the Tractus opticus (2V. op.), and corresponds with the Sulcus limitans 

 between the tJicdatrms and the striatum. 



Crossing the crus {Or. cb.), just caudad of the postgeniculatum {pgn.), is seen the 

 cimbia (cmb.). 



" Upon this figure should appear the Lemniscus superior and L. inferior, and the post- 

 bracMum and prcebracMum, provided they exist in the cat as distinct parts visible at the 

 surface. I have not been able to satisfy myself respecting their exact position and limits 

 in the human brain, and refrain from expressing any opinion concerning them." 



§ 1168, Fig. 10. — The dorsal aspect of the diencephalon, including the diatela. 

 From Prep. 301, a half grown J ; x 1. 



The object of this figure is to show the existence of a distinct roof of the diacaiia inde- 

 pendent of the fornix and velum, which have been removed. This diatela (dtl.) presents 

 the appearance of something more than the lining endyma, but its structure has not, 

 so far as we know, been examined. The darker triangular area at the cephalic end of 

 the diatela corresponds with the delta fornicis {dlt. /.). 



§ 1169. Fig. II. — The Area cruralis, with part of the pons and of the Ar. praechi- 

 asmatica. From Prep's 506, 435 (nearly adult ? ) and 461 ( J ) ; x 1.5. 



This figure, reversed, is reproduced in outline in Fig. 118. The general relations of the 

 medicornu are also indicated in Fig. 113, and the relations of the cornu, rima and pro- 

 plexus in Fig. 131. 



The Lobi temporales have been divided at different levels on the two sides. From 

 the right, only the extremity, or LI. hypocampm, has been removed, and the section of the 

 medicornu (mcu.), which is here cut very obliquely, is a slightly curved space completely 

 circumscribed by a nervous wall. Neither in the cat, nor — contrary to the common belief 

 and the explicit statement in Quain (A, II, 543, 544) — in man, does the rima or " great 

 transverse fissure " extend to the tip of the medicornu. 



Where the LI. hypocampm rests against the Tractus opticus (TV. op.), there is usually 

 a deep notch which may be called the Incisura hypocampae (Inc. hmp.). 



On the left side, the hemisphere was dissected off so as to leave two cut surfaces. One 

 of these surfaces is plane and nearly horizontal , and lies at about the level of the dorsal 

 end of the postgeniculatum (pgn.). The other is convex, and extends from the cephalic 

 border of the former obliquely to the ventral surface of the brain ; it corresponds closely 

 ■with the cephalic border of the Tractus opticus. 



