PINEAL REGION IN MAMMALIA 85 



paraphysis, he states that no glandular structure was present 

 in his specimens but that the paraphysal arch was in all cases 

 well defined. The velum was also clearly traceable in his em- 

 bryos and my own observations as to the velum and the para- 

 physal arch coincide with his results. I have been able, how- 

 ever, to demonstrate the presence of a paraphysis. It exists 

 in a rudimentary form as compared with that of lower verte- 

 brates and is very inconstant. Out of the embryos in the Har- 

 vard collection used in the preparation of this paper I have been 

 able to find it in only eight cases. These specimens were em- 

 bryos in good preservation and a,ny that were at all damaged in 

 the region of the forebrain were excluded, though two or three 

 of these showed signs of a possible paraphysal outgrowth. It 

 is owing to the relatively large number of human embryos in 

 the Harvard Collection that the writer was fortunate enough to 

 find the few specimens containing a paraphysis, which will here 

 be described. 



In an embryo of 15 mm. (fig. 12), a shght median elevation is 

 seen in the paraphysal arch in the true morphological position 

 of a paraphysis. It is composed of a soUd clump of cells with 

 no cavity with the exception of a very tiny dimple on the under 

 side of the arch just beneath it A similar structure could be 

 found in other embryos of about the same size, H. E. C. no. 2044, 

 16 mm. and H. E. C. no. 1707, 16.4 mm. From the above 

 stages up to embryos of 23 mm. no signs of a paraphysis could 

 be found with the exception of thi-ee doubtful cases in embryos 

 of 19 to 20 mm. which were, however, excluded as the roof of 

 the forebrain was somewhat damaged. In an embryo of 23 

 mm. (fig. 13), however, a tiny paraphysis with a slight cavity 

 is clearly seen. This model was made from a sagittal series and 

 the paraphysis only extended through four sections and was at 

 first overlooked. Three other embryos of approximately this 

 same size showed no signs of any paraphysal outgrowth and 

 had a simple paraphysal arch as shown by Bailey (2), figure 18. 



Figures 14, 15 and 16 are taken from two models of the para- 

 physal and velar region of the roof of the forebrain of an embryo 

 of 25 mm. This embryo was in an excellent state of preserva- 



