I04 Journal of Comparative Neurology. 



Figs. 4 and ^. Epencephal of an embryo kitten i8 mm. long, No. 3338 

 (x 15). Fig. 4, dorsal aspect, shows, 



a. General form of the epencephal, constricted at the isthmus, widened 

 caudad. 



b. The roof-plate (or deckplate) which being thinner than the lateral parts 

 of the roof has been forced dorsad in the form of a longitudinal fold as the 

 brain hardened and contracted slightly. 



c. The lateral U-like bend of the substantial parietes which projects lat- 

 erad from the brain tube and has resulted from the folding of the tube upon it- 

 self at the pontile flexure. It appears to have been formed as a result of the 

 flexion of the tube and the concomitant growth of the parts concerned, so that 

 there results a U-shaped bend which projects laterad like an ear from the 

 brain tube. Fig. j shows the lateral aspect of the bend. 



d. The two lateral protons of the cerebellum which have not yet fused at 

 the meson. It is interesting to note that these two structures have rotated so 

 that they stand up dorsad at nearly right angles to the brain tube. See Figs. 

 29, 30, 31, PI. III. 



e. The caudal fold which is formed as a result of the lateral U-bend, cdl. 

 fd. The lateral wall is doubled upon itself, so that a fold is projected entad 



and in this manner forms the floor of the parepiccele, and apparently develops 

 into the auditory eminence of the adult. I have indicated this structure in the 

 earlier embryos by the term auditory region. See Figs. 8, 10, 12, 13, PI. I, Fig. 

 35, PI. Ill, and Figs. 52, 53, 54, PI. V. 



f. The relations of the tela which forms the roof of the metacoele and the 

 dorso-caudal wall of the parepicceles. The tela has been torn away on the left 

 side so as to expose the cavities and the ental surface of the cerebellum. The 

 heavy black line represents the ripa, the torn edges of the tela. The mem- 

 branes are shown entire on the right side. 



Fig. 5. Shows the lateral aspect of the same embryo. The mesencephalic 

 roof is seen to extend both cephalad and caudad. The caudal extension rapidly 

 increases, so that in embryos a little older, it reaches almost to the caudal bor- 

 der of the epencephal. The dorsal fold of the metatela which dips down deep 

 into the metaccele is also clearly shown. Compare Figs, 31 and TjT,, PI. Ill, 

 mtplx. 



Figs. 6 and y. Embryo kitten 23 mm. long. No. 3339 (x 15). Shows the 

 same general features as, Figs. 4 and 5, and in addition, 



a. The still greater caudal extension of the mesencephalic roof. 



b. The increased size of the two protons of the cerebellum which have 

 not yet fused at the meson. A peculiar notch or fold marks their mesal extrem- 

 ity. This notch is, perhaps, an artifact due to the shrinking of the brain dur- 

 ing hardening. The caudal (ental) surfaces of the cerebellum are not shaded to 

 represent them more clearly, but it must be remembered that they are covered 

 by the tela and are therefore within the proper brain cavity [i. e., they are en- 

 tocoelian surfaces). For the sake of clearness, the kilos and the ripa or the 

 line where the kilos ends and the metatela begins have not been shown. The 

 ripa is approximately just caudad of the place where the shading ends. 

 The line caudad of the shading represents the line of the attachment of the 



