338 THE PINEAL ORGAN 



Texas — the foramen is very small, and it is also small in Palceogyrinus — 

 Carboniferous — and in Trematosaurus. In the latter the foramen is 

 situated far back in the roof of the skull behind the central point of the 

 interparietal suture. 



In the adult skulls of living Anura {Rand) and living Urodela (Molge) 

 the pineal foramen is usually absent, although a slight depression is 

 visible on the dorsal aspect of the skull, in the usual situation of the 

 foramen in the skull of Cryptobranchus japonicus. 



Since some of the extinct Labyrinthodonts were of gigantic size — the 

 skull of L.Jcegeri measuring more than 3 ft. in length and 2 ft. in breadth — 

 it may be presumed that the actual size of the pineal eye was proportion- 

 ately large and also more highly differentiated than in modern Amphibia, 

 in which the terminal vesicle is constricted off during the larval or tadpole 

 stage of development by the growth of the skull, and since it is completely 

 separated from its connection with the brain it can have no function as a 

 visual organ. 



It is in some of the extinct carnivorous reptiles of the Mesozoic period 

 that the pineal foramen attained its maximum size, both relatively to the 

 size of the skull in some of the smaller animals and actually in some of 

 the larger types, such as the Ichthyosauri — Lias, Oolitic, Chalk (Fig. 190, 

 Chap. 20, p. 268). It was also large in the mammal-like or Theromorph 

 reptiles, including Titanosuchus, in which the diameter of the foramen 

 was approximately 1 centimetre (Watson) (Fig. 237). 



The foramen is more circular in the primitive flat-headed types such 

 as Conodectes (Permian), Captorhinus, and Procolophon (Fig. 171, Chap. 19, 

 p. 237). It is more oval in form in those types in which the cranial cavity 

 is narrowed in association with elongation of the skull and a high degree 

 of development of the temporal fossae with their contained masticatory 

 muscles, as in the Anomodont reptile Dicynodon (Broom) (Fig. 205, p. 300). 

 In Dicynodon the canines were very large, and in the dog-toothed Cynodont 

 reptiles in which incisor and molar teeth were also present both these 

 and the canines were well developed. Moreover, associated with this 

 development of the teeth there was a corresponding development of the 

 masticatory muscles, including the temporals, which grew upwards over 

 the roof of the skull, where they became attached to a median sagittal 

 crest, within which was the pineal canal. Finally, as the muscles increased 

 in size and the crest became deeper and narrower, the pineal canal within 

 it became obliterated, as in Ictidosaurus (Fig. 233, p. 332). 



Having referred to the regressive changes which have occurred in the 

 pineal system, during the period which has elapsed since the Palaeozoic 

 era, in the sub-classes Teleostomi and Dipnoi, with special references to 

 the supposed origin of the amphibians and reptiles from extinct repre- 



