PINEAL EYE IN LAOEETILIA. 165 



On the Presence and Structure of the Pineal 

 Eye in Lacertilia. 



By 



fW. Bald'Yvin Spencer, B.A., 



Fellow of Lincoln College, Assistant to the Linacre Professor of Human and 

 Comparative Anatomy in the University of Oxford. 



With Plates XIV, XV, XVI, XVII, XVIII, XIX and XX. 



The following work has been carried on in the morphological 

 laboratory of the University of Oxford. It has been made 

 possible solely through the kindness of Professor Moseley^ 

 whose invaluable assistance in various ways, especially in 

 procuring from different sources the necessary specimens, I 

 here desire to acknowledge with sincere thanks. 



Historical Account. — Though it was impossible for the 

 external indication of the important organ which forms the 

 subject of the following pages to escape the notice of naturalists 

 and more especially of those dealing with the classification of 

 the group, consisting as it does in the modification of a median 

 scale upon the dorsal surface of the head, yet it is strange that 

 only within a very recent period has there been any thorough 

 investigation of the structures lying beneath. This is perhaps 

 chiefly to be accounted for by the fact that the structure in 

 question lies usually within the parietal foramen, enclosed 

 tightly by bone and connective tissue, and is thus left intact 

 within the skull on removal either of the skin from the external 

 or the brain from the internal surface. 



Brandt,^ writing in 1829, uses the following words when 

 describing the skull of Lacerta agilis. " Hinterhaupts- 

 > ' Medizinisch Zoologie,' 1829, Bd. i, p. 160. 



