236 THE PINEAL ORGAN 



close together on the top of the head, and a relatively small parietal 

 foramen lies some distance behind them. In other cases (Fig. 169) the 

 skull is narrow, as in Dolichosoma longissimum, found in the lower Permian, 

 Bohemia. In this the parietal foramen is of moderate size and the frontal 

 and parietal bones are fused in the median plane, and are partially fused 

 with each other, so as to form a fronto-parietal plate, as in living types. 

 In the primitive type Branchiosaurus amblystomus and in Protriton (Fig. 

 170) the parietal foramen is relatively very large, and the parietal and 

 frontal bones are separate. This is the case also in Eryops megacephalus 

 and Capitosaurus (Fig. 171, B). A special feature of some of the primitive 

 types such as Protriton (Fig. 170) is the presence of circumorbital bones 

 excluding the frontal bone from participation in the formation of the orbit 

 and a ring of sclerotic plates for the protection of the eye within the orbit. 



pmx 



pmx 



-fr 



(jri 



"1 1M 



A SQ/ B ^ 



P a so 



Fig. 169. 



A — Dorsal aspect of skull of Metanerpeton pulcherrimum, showing the broad type 

 of head with separate parietal and frontal bones. (Fritsch 1 1, after Credner.) 



B — Dolichosoma longissimum, showing narrow type of skull with fused parietal and 

 frontal bones. Lower Permian, Bohemia. 31. (After Fritsch.) 



ep. : epiotic. 



fr. : frontal. 



ju. : jugular. 



mx. : maxilla. 



na. : nasal. 



Orb. : orbit. 



pa. : parietal. 



pi.f. : pineal foramen. 



pmx. : premaxilla. 



po. : postorbital. 

 Po.f. : postfrontal. 

 pr.f. : prefrontal. 

 Qu. j. : quadratojugal. 

 50. : supraoccipital. 

 sq. : squamosal. 

 st. : supratemporal. 

 x. : anterior. 



A general consideration of the skull of labyrinthodonts in all six orders 

 of which a conspicuous parietal foramen is present, while it appears to 

 be generally absent as a recognizable feature in macerated skulls of modern 

 amphibians corroborates the impression gained by the study of the parietal 

 foramen in fishes, namely, that its presence as a relatively or actually 

 large foramen in the skulls of the more ancient types of fossils and the 



