ON THE MORPHOLOGY OF THE PINEAL REGION, BASED 

 UPON ITS DEVELOPMENT IN ACANTHI AS. 



CHARLES SEDGWICK MINOT, LL. D. 

 From the Embryological Laboratory of the Harvard Medical School. 



With 14 Text Figures. 



The term "pineal region'" is used here in a descriptively topo- 

 graphical sense, the observations reported concern the epiphysis, para- 

 physis, vehim transversum, and the superior and posterior commissures 

 chiefly in dog-fish embryos of from 11.5 mm. to 86.0 mm. The sec- 

 tions studied form part of the Harvard Embryological Collection, the 

 general plan of which I have briefly described in an earlier article.' 

 To facilitate confirmation of the observations the number of the embryo 

 and of the section, as catalogued, is given for each of the illustrations. 



Our previous knowledge of the pineal region in Elasmobranchs is 

 based on the observations of Balfour {Worls, Vol. I, p. 399 ff.) and 

 Ehlers, 78.1, on the development, and of Ehlers and Cattie, 81.1, on 

 the adult anatom3^ Cattie reviews the earlier literature quite thor- 

 oughly. Gaupp's resume, 98.3, in the " Ergehiisse " is invaluable for 

 the comparative study of the parts. The account of the development 

 of the epiphysis proper, given by Balfour and Ehlers is essentially cor- 

 rect. They both saw the velum transversum, but did not specially 

 study it. It has been more accurately figured by W. His, 92.1, p. 361, 

 Fig. 14. Balfour figures only the superior commissure, which he 

 identified as the posterior, and appears not to have observed the true 

 posterior commissure at all. Ehlers, 78.1, has indicated both commis- 

 sures in his Fig. 8, very clearly, but gives no description of their de- 

 velopment in his text. Neither Ehlers nor Balfour mention the para- 

 physis, which was not recognized as a morphological constituent of the 

 brain until much later (Selenka, 90.1), but Balfour has recorded several 

 of the changes in the paraphysal region. Balfour's descriptions of the 

 pineal region are incomplete, and owing to the defective methods of 

 the time, often inexact as to details. 



In embryos of Squalus acanthias of 11.5 mm. in length " the changes 



1 Anatomischer Anzeiger, Bd. XVIII, pp. 138-139. 



'^ The measurements of lengths are from the preserved specimens in alcohol. 



