98 JOHN WARREN 



the paraphysal arch, somewhat similar to the condition in 

 rodents, which hes in the morphological position of the true 

 paraphysis. Of two specimens of cow embryos one of 17 mm., 

 sagittal series, H. E. C. no. 1126, showed beautifully all the 

 primary subdivisions in the roof of the forebrain, and the older, 

 a transverse series, was not reconstructed. The same is true of 

 several early deer embryos which at 7 to 9 mm. showed the 

 arches and subdivisions of the forebrain as previously described. 

 See H. E. C. no. 1514, 9.8 mm. sagittal series and H. E. C. no. 

 1516, 7.3 mm. transverse series. The oldest deer embryo of 

 18.6 mm., H. E. C. no. 1230, had a very rudimentary epiphysis, 

 velum and paraphysal arch and no sign of any paraphysis. 



Jf.. Carnivora 



A. Dog. yOi the thi'ee sets of sagittal sections in the collec- 

 tion those of 14 mm. and 17 mm. are here shown, as the young- 

 est, 12.5 mm., was somewhat damaged in the paraphysal region. 

 Figure 31 is a median section of the forebrain of the 14 mm. 

 embryo and shows the primary arches, although the postvelar 

 arch is already somewhat invaded by the plexus, which was not 

 the case in the 12 mm. embryo. The velum forms a well devel- 

 oped fold with a low paraphysal arch in front. On the dien- 

 cephalic side of the velum the velar end of the roof plate bulges 

 somewhat forward over the velum. It should be noted that 

 the posterior commissure has filled nearly the whole of the pars 

 intercalaris and extends practically up to the low epiphysal 

 arch. In figure 32, embryo of 17 mm., there is no sign of a 

 paraphysis, the velum forms a sharp fold and the diencephalic 

 roof protrudes above it in a pouch-like projection very similar 

 to what is seen in a median section of some of the human em- 

 bryos. This pouch makes a fold extending across the whole 

 width of the roof. Owing to lack of material it was impos- 

 sible to follow the development further, but it can be stated 

 that the primary arches are present and that there is a hint of 

 the diencephalic outgrowth described in human embryos. 



B. Cat. The primary arches in cat embryos are quite similar 

 to the pictures abeady shown here in other forms and there is 



