THE PINEAL SYSTEM OF OPHIDIA 285 



taceous, Kansas. These were marine, lizard-like animals of large size 

 (5 metres), having anterior and posterior paddles adapted for swimming. 

 The parietal foramen of Platecarpus was oval in outline, the longest 

 diameter being about 2 cm., it was in the median plane and situated at 

 the anterior border of the triangular parietal bone, immediately behind 

 the frontal bone. Although possessing certain characters which differ- 

 entiate them from the Lacertilia, the Pythonomorpha or Mosasaurida: 

 are more nearly allied to lizards than the snakes, and fossil skulls of the 

 true Ophidia which are of comparatively recent date do not appear to 

 differ markedly from the skulls of living species. 



The pineal system of living examples of Ophidia has been studied by 

 Sorensen, 1894 5 Leydig, 1897 '■> Studnicka, 1893 5 an ^ Rabl-Riickhard, 

 1894. The epiphysis of the common ringed snake, Tropidonotus, a non- 

 poisonous British species, is developed as a simple hollow evagination from 

 the roof of the diencephalon in the usual situation between the habenular 

 and posterior commissures, and there is usually a well-developed para- 

 physis and dorsal sac. Later it becomes pear-shaped, and eventually the 

 cavity disappears in the distal part, which becomes a solid rounded mass, 

 and at the base, where the neck becomes constricted and cord-like. 

 What appears to be a remnant of the original cavity may, however, 

 persist at the junction of the stalk with the body of the organ (Fig. 179, 

 Chap. 20, p. 251). 



In the adult the body is surrounded by blood-vessels which penetrate 

 into its substance and produce a lobulated appearance. The whole is 

 enclosed in a sheath consisting of an inner and outer layer of connective 

 tissue, which is continuous with the pia mater and encloses a space. 

 Leydig described a striated appearance in the pedicle, which he thought 

 was produced by nerve-fibres connecting the organ with the posterior 

 commissure. In one case the distal end of the organ was surrounded by 

 deeply pigmented cells. Studnicka considered that the lobulation and 

 penetration of the organ by connective tissue septa containing capillary 

 blood-vessels might be an indication of its transformation into a gland 

 of internal secretion. It is quite common, however, to find degenerating 

 nervous or neuroglial tissue invaded by blood-vessels, and the appearance 

 is very different from that of a typical endocrine gland. 



The Pineal System of the Chelonia. 



The parietal organ and parietal foramen are lacking and the pineal 

 organ is represented merely by a rudimentary epiphysis. 



The development of the parietal region of the brain has been studied 

 by Voeltzkow (1903) in Chelone, and in Chelydra serpentina, the snapping 

 turtle, by Humphrey (1894). Voeltzkow found that in the early embryonal 



