1 82 



THE PINEAL ORGAN 



Upper Devonian of Ohio (Fig. 131) and in that remarkable extinct Elasmo- 

 branch fish Pleuracanthus (Fig. 141, B, p. 201). Examples of the latter 

 have been found in the Carboniferous and Permian periods, and it would 

 seem that a complete parietal foramen previously present in this plate had 

 already disappeared at a date which preceded these two periods. The 

 more primitive condition, namely, the presence of a parietal foramen, seen 

 in the two examples cited, is thus exemplified in a living animal, the 



p imp. 



Fig. 131. — Head-shield of Dinichthys intermedius. (After A. S. Wood- 

 ward.) 

 A — Upper surface. 



B — Intracranial surface, the latter showing a well-defined pineal impression, 

 from the upper Devonian of Ohio, U.S.A. 



p. imp. : pineal impression. p. pi. : pineal plate. 

 orb. : orbit. 



lizard ; whereas the closed foramen, indicating a complete loss of visual 

 function and atrophy, is seen in the fossil fish. In the still more ancient 

 fish Osteolepis, however, a well-marked pineal foramen is present in a 

 plate formed by the fusion of the two frontals and lying between the orbits 

 (Fig. 132). 



Definition of Terms applied to Structures in the Parietal 

 Region of the Brain 



1. Paraphysis (Fig. 130). — This is a sac-like evagination of the roof 

 of the interbrain, which arises at the junction of the lamina supra- 

 neuroporica and the inwardly projecting transverse fold, the velum 

 trans versum. The walls of the paraphysis which at the commencement of 



