302 THE PINEAL ORGAN 



in other respects it is much more reptilian in character, serves as an example 

 of the earlier type of fossil reptile-skull, in which the parietal foramen 

 lies in the suture between two horizontally placed parietal bones, which 

 are separated from the single temporal fossse merely by a backward pro- 

 longation of the postorbital. This bone is reduced in Glochinodontoides, 

 and the parietal bone shares in the formation of the temporal fossa, as 

 it does in the human subject and other living orders of mammals. 



Development of the Pineal Organ of Mammals 



Despite the wide differences in the general form and structure of 

 adult types of mammalia, the early stages of development of the pineal 

 organ appear to be very similar in all. We shall therefore give a short 

 description, in the first place, of the development of the human pineal 



Fig. 207. — Median Linear Reconstruction of thf Pineal Region and 

 Posterior Commissure of a 20-MM. Human Embryo. The Apex of the 

 Pineal Diverticulum is directed Forward. (R. J. G.) 

 Ant. D. : anterior diverticulum. N.Z. : nuclear zone. 



Aq. C. : aqueductus cerebri. M.Z. : marginal zone. 



Ep. : ependyma. P.C. : posterior commissure. 



Epd. : epidermis. Post. D. : posterior diverticulum. 



V. III. : third ventricle. 



organ, of which we have a more complete knowledge than of other types, 

 and will only refer to the development of the pineal system in lower 

 mammals with respect to any corroborative evidence or peculiarity of 

 structure which may be of general interest. 



One of the first indications of the development of the pineal system 



