1881.] «^55 [Wilder. 



The entire Area cruralis may be more completely exposed by removing 

 the cerebellum and dorsiducting the medulla, as in prep. 425. 



Fig. 12. — The dorsal aspect of the Metencephalon or Medulla, showing 

 the metatela or roof of the metacoelia. From prep. 397, adult 9> 464 and 

 491. 



The metatela here shown is apparently independent of thep^■a; like the 

 diatela it seems to consist of more substantial tissue than simph^ endyma, 

 but I am not aware that its microscopic structure has been ascertained. I 

 am in doubt respecting the precise limits and attachments of the metatela, 

 and the form and location of the "foramen of Magendie." Hence the 

 figure is vague and unsatisfactory upon these points. 



Fig. 13. — Part of an oblique transection of the Prosencephalon and 

 Diencephalon to show the form and position of the crista. From prep. 441. 

 Enlarged two diameters. 



The brain was transected obliquely at an angle of about 45 degrees with 

 the general longitudinal axis. The plane of section passed from a point 

 nearly dorsad of the genu, through the aula, the medicornua and the albi- 

 cantia. The figure includes only a part of the caudal aspect of the slice. 



The dorsal borders of the hemispheres are divaricated slightly, and the 

 callosum (cl.) is seen crossing the interval ; the slight notch on each side 

 just dorsad of the callosum is the F. callosalis [F. d.). 



The striata (s. s.) are seen in section just ventrad of the lateral expan- 

 sion of the callosum, while the lower part of the figure is occupied by the 

 thalami (tJi), united by the meclicomniissura (mcs.). Between each thala- 

 mus and the corresponding striatum is a groove, the Sulcus Umitans 

 {81. li.). 



The Golumnm forntcis (Glin. f.) are divided nearly at a right angle with 

 their course, and at a point just dorsad of the crista (crs. /.), which is par- 

 ticularly well shown in this preparation. The open space between the 

 fornix and the thalami is the aula (a.), and on each side are the portce (p.) 

 leading into the procodim. All the plexuses have been removed. 



PLATE IV. 



Unlike those of Plate III, all of the figures upon this plate represent cut 

 surfaces, although some natural surfaces are shown also. 



Fig. 14. — k. ventricaudal view of the fornix, with the adjacent parts. 

 From prep's. 507, 463 and 396 (adult J''). Enlarged two diameters. 



The preparations were made while the brain was fresh, so as to permit 

 more flattening of the hemispheres, and consequent exposure of the fornix. 



After the removal of the rhinen., meten., epen. and mesen., the thalami 

 and geniculata were excavated piecemeal, so as not to injure or displace 

 the fornix. The cut surface (.«.) at each side of the fornix (/".) is the plane 

 of division of the dien . from the striatum. 



The cephalic end of the prosen was then sliced down to the level of the 

 jircecommissura (prcs.), which is seen to send a distinct fasciculus toward 

 the rhinen. on each side. Then the right hemisphere was sliced obliquely 



PKOC. AMER. PHILOS. SOC. XIX. 109. 3k. PRINTED DECEMBER 28, 1881. 



