io6 Journal of Comparative Neurology. 



dicated by the heavy black line, rp. The auditory region shows a marked in- 

 crease in size. At this stage the paraflocculus is larger than the prepileum. 

 The figure does not show the cerebellar peduncle which is just beginning to 

 form. See Fig. 14. 



Fig. 12. Shows the dorso-caudal aspect of the cerebellum of an embryo 

 kitten 53 mm. long (x 7-5) • This is practically the same condition as that 

 shown by a human embryo, Fig. 60, pi. VI. The raesal part of the cerebellum 

 is still quite thin, and four distinct furrows are present. The nodular sulcus is 

 unmistakable and in addition to the parafloccular sulcus, a new furrow, the in- 

 terpilear sulcus, has appeared. There is a corresponding sulcus upon the other 

 side of the cerebellum. These sulci do not cross the meson and apparently do 

 not become continuous with any of the mesal sulci which appear later. The 

 interpilear sulcus divides the pileum into two regions which appear to be dis- 

 tinct through life. The parepicoele and caudal fold are shown very clearly. 

 The specimen is turned at such an angle that the caudal projection of the cere- 

 bellum does not show. Tela and plexus have been removed. The heavy black 

 line indicates the ripa. 



Figs . jj and i^. Cerebellum from an embryo kitten about 55 mm. long, 

 No. 3341 (x 7.5). Shows a later stage of development ; two new furrows are 

 present — the furcal sulcus and the uvular sulcus. I have not been able to ob- 

 tain specimens to show which one appe.ars first. But the adult condition indi- 

 cates that it is the furcal. See Fig. 44, PI. IV. The furcal sulcus divides the 

 mesal portion of the cerebellum transversely into two unequal parts. For rea- 

 sons to be stated elsewhere we shall call all oi the organ which lies cephalad of 

 the %w\zv.s, prerannis, and all that lies caudad postrannts. In addition to the fea- 

 tures just noted the figure shows essentially the same parts as Fig. 12. 



Fig. 14. Left lateral aspect of the same specimen. Shows very clearly 

 the caudal extension of the mesen. Compare Figs. I, 5, 7, 9. The peduncle 

 of the cerebellum is now recognizable The specimen also shows the relation 

 of the interpilear sulcus to the parafloccular sulcus and the relation of the pre- 

 pileum to the postpileum ; the former now has a volume greater than that of 

 the paraflocculus. The kilos, ripa, and plexus show plainly. 



PLATE II. 



Figs, i^ and 16. Cerebellum of an embryo kitten 63 mm. long, No. 3342, 

 (x 7.5). Shows practically the same features as Figs. 13 and 14, PI. I. In add- 

 ition to these there appears a slight elevation surrounded by a very shallow 

 groove,' the interpileum. (This term was suggested by Professor Wilder.) 

 The structure forms an interruption between the interpilear and the uvular 

 sulci. At present I am unable to explain its significance, but shall discuss it in 

 a future paper, as soon as enough material is available. The mesal shading in- 

 dicates a depression extending cephalo-caudad. 



Fig. j6. Left lateral aspect of the same specimen. 



IThe lines surrounding the interpileum in Fig. 15 should not have been quite so heaTy, 

 They represent only a very shallow groove, not a sulcus. 



