Stroud, Mammalian Cerebellum. 109 



Figs. 2^, 26, 2y, 28 are oblique transections of the brain of an embryo 

 kitten about 12 mm. long and show a very early condition, a little farther ad- 

 vanced however than Figs. 24 and 24a. The sections are as nearly transections 

 as I could cut them ; but every one knows how difficult it is to section so small 

 an embryo exactly at right angles to the meson. 



Fig. 23. Section through the isthmus. The left side includes a little of 

 the mesencephal. It also shows the thickening of the wall at the isthmus and 

 the general arrangement of the brain at this point. 



Fig. 26. A transection through the epencephal cephalad of the cere- 

 bellum. 



Fig. 27. A transection through the cerebellum ; includes the cephalic part 

 of the lateral U-bend. Compare Figs. 5 and 7, PI. I. This stage of develop- 

 ment is of the highest morphological interest because it shows, • 



a. That the lateral parts of the caudal portion of the epiccelian roof are 

 thick, while the mesal part is thin at the deckplate. 



b. The lateral pprts are clothed with cinerea which does not extend across 

 the meson (compare Figs. 4 and 6, PI. I); this proves conclusively that the cere- 

 bellum is developed from the two lateral areas, or protons, which by a kind of 

 proliferation gradually extend mesad till they form a continuous thickened mass. 



The dorsal projecticm at the meson is an artifact due to collapse of the 

 brain during the process of hardening and infiltrating with collodion. The 

 linelaterad of the U-bend represents the tela which forms the lateral wall of the 

 parepicoele. 



Ftg. 2S. A transection of the same embryo through the mesencephal, 

 showing the general character of the metatela and kilos. 



Figs. 2g, JO, ji, jij, are sagittal sections of the epencephal of an embryo 

 kitten 18 mm. long. 



Fig. 29 is a section near the lateral extremity of the lateral U-bend and 

 shows, 



a. The parepicrele. 



b. The beginning of the plexus. 



c. The extreme lateral end of the cerebellum and the auditory region, 



d. The relation of the kilos and tela to the cerebellum at this extreme lat- 

 eral point. Compare Figs. 4, 5, 6, PI. I, also Figs. 50, 53, and 54, PI, V. 



Fig. JO is a section a few microns farther mesad. It shows essentially the 

 same conditions as Fig. 29. 



Fig. 31. Section still farther mesad. Shows, 



a. The dorsal rotation of the cerebellum to a position nearly at right an- 

 gles with the brain axis. 



b. The kilos both at the caudal (here dorsal) edge of the cerebellum and 

 around the edge of the metencephal. 



c. The metaplexus. 



The condition here is apparently comparable to that found in certain rep- 

 tiles, Herrick (13, 7). The black line, endyma, is a continuation of the cells 

 forming the plexus. 



Fig. jj. Shows the mesal aspect of the same specimen. Note the general 



