1881.] 55d [Wilder. 



shown here as a nearly regular circular spot ; in reality, it presents a slight 

 mesal extension at both the dorsal and ventral sides. Indeed, when care- 

 fully examined, the so-called "aquseductus sylvii" is far from being a per- 

 fectly 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 coelia, with 

 lateral extensions. 



The cimhia {cmh.) is partlj^ seen on the right. The geniculata {pgn. and 

 X>rgii.) do not project as far as they should. The optici are wholly hidden 

 from view by the \)YOuAnenX postoptici (pop.). 



Fig. 9. — The sinistral aspect of tlie Mesencephalon and Diencephalon. 

 From preps. 491 and 506. Enlarged two diameters. 



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

 transection between the dien. and the prosen. ; the plane of section fol- 

 lowed the cephalic border of the Tractus opticus {Tr. op.), and corresponds 

 with the Sulcus Umitans between the thalamus and the striatum. 



Crossing the crus {Gr. cb.) just caudad of the jjostgeniculatum (pgn.) is 

 seen the cimhia (cmb.). 



The ISfervus trochlearis {N. tr.) had been removed from prep. 506, and 

 was added from prep. 491. 



Upon tliis figure should appear the Lemniscus superior and L. inferior, 

 and the jjostbrachium emd prmbrachium, 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. 



Fig. 10. — The dorsal aspect of the Diencephalon, including the diatela. 

 From prep. 301, a half grown (^. 



Tlie object of this figure is to show the existence of a distinct roof of the 

 dinccelia independent of the velum, whicli has been removed. This diatela 

 (dtl.) presents the appearance of something more than the lining endyma, 

 but its structure has not, so far as I know, been examined. The darker 

 triangular area at the cephalic end of the diatela corresponds with the 

 delta for nicis (dlt.f). 



Fig. 11. — The Area cruralis, with part of the pons and of the Ar. pre- 

 chiasmatica. Enlarged two diameters. From preps. 506, 425 (nearly 

 adult 9) and 461 (J). 



So small and so numerous are the parts shown in this figure, that it 

 should have been yet more enlarged. 



The Lobi temporales have been divided at diflereut levels on the two 

 sides. From the right, only the extremity, or LI. Jiypocampce, 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 ner- 

 vous 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 fissui'e " extend to the tip of the medicornu. 



Where the LI. liypocampcs rests against the Tractus opticus {Tr. op.). 



