198 W. BALDWIN SPENCER. 



were cut, to he closed. Its position is indicated by a large 

 blood-vessel which branches on the internal surface of the skull 

 as it enters the bone exactly as the vessel accompanying the 

 pineal stalk branches on entering the parietal foramen, the two 

 branches thus formed pass through to the external surface. 

 The parietal foramen appears simply to have closed up, the 

 blood-vessel remaining and piercing the bone. 



In many forms such as Leioloemus the optic vesicle is 

 placed quite on the internal side of the foramen ; in such a 

 form as this were the bone to grow and close up the foramen 

 the vesicle would be left on the internal surface ; this is exactly 

 what appears to have taken place in Ceratophora aspera. 

 The epiphysis has the usual form, being well developed and con- 

 sisting of a proximal portion at right angles to the roof of the 

 thalamencephalon, whilst, from the further end, the distal 

 portion runs forward along the under surface of the dura mater 

 as the pineal stalk until it ends in a slightly swollen portion 

 immediately beneath the parietal foramen. This corresponds 

 to the optic vesicle of other forms ; in structure it appears to be 

 solid and to consist of rounded elements, resembling very closely 

 those present and figured by de Graaf in Ran a esculent a. 



There is this important difference, however, between Amphi- 

 bia and Lacertilia, that in the former the distal portion of the 

 epiphysis becomes completely cut off from the proximal and is 

 placed externally to the skull, whilst in Lacertilia, on the other 

 hand, the distal part not only remains in connection with the 

 proximal but is permanently closed within the skull cavity 

 after closure of the parietal foramen. 



Lyriocephalus scutatus. 



The usual external indication is present though not so pro- 

 minent as in many other forms, the scale being somewhat 

 smaller than those by which it is enclosed posteriorly, which 

 form a v-shaped ridge behind it, the point of the v being di- 

 rected backward ; on the scale a circular, slightly raised, trans- 

 parent part is modified to form a cornea. 



Internally the structure of the optic vesicle resembles more 



