88 JOHN WARREN 



In thi^ee or four other embryos of approximately this same size 

 a similar formation could be seen which in some cases was carried 

 still further forward into a finger-like projection in the mid-line, 

 which gave in the section the impression of a small rounded tube 

 whose walls were rather thicker than the diencephalic roof. 

 The embryo of 25 mm., a median section of whose brain is seen 

 in figure 14, shows this projection more distinctly. Figure 15 

 gives an external view of the same specimen, where the details 

 of the tubules can be clearly seen. There are two main pouch- 

 like projections on either side of the mid-line, which show a 

 tendency to give off smaller tubules and to cover up the para- 

 physis. They are limited below by the fold in the brain wall 

 formed by the velum and have quite definite limits above, the 

 extreme lower end of the postvelar arch being alone concerned 

 in this formation. Their relations to the brain cavity are best 

 seen in figure 16, which gives a view from the interior of the 

 brain. In the lower part of the figure is the lamina terminalis, 

 L.T., which passes over into the forebrain roof, T.R.P. The 

 opening of the paraphysis, P, lies just cephalad to the velum, 

 V, and there can be no doubt of its telencephalic origin. On 

 the diencephalic side of the velum appear the two large pouches 

 in the depths of which are the openings of the smaller tubules. 

 This outgrowth as a whole begins at the diencephalic lip of the 

 velum, involves practically the whole width of the postvelar 

 arch at this point and ends fairly definitely above. Beyond this 

 point the diencephalic roof arches upwards with a perfectly 

 smooth and gently curved surface. This structure is clearly 

 of diencephalic origin and should never be mistaken for the 

 paraphysis. 



Embryos of 28.8, 29, 30, and 31 mm. were next examined and 

 in all of them some similar formation was to be seen, which 

 varied from a relatively simple fold like that in figure 13 to a 

 more complicated replica of what has just been described. The 

 embryo of 31 mm., H. E. C. no. 1706, was selected in order to 

 show the separation of some of the tubules from the brain and 

 their formation into blind cysts or vesicles. Figure 17 shows a 

 model of this embryo seen from the front, as is the case with 



