THE PINEAL SYSTEM OF VERTEBRATES l8l 



(3) The dorsal sac. Tela chorioidea superior. 



(4) The habenular commissure (commissura superior). 



(5) The pineal organs, including : 



(A) The pineal eye or parietal organ. 



(B) The " parapineal organ." 



(C) The connections of these organs with the central nervous 



system. 



(6) Pars intercalaris (Schaltstiick). 



(7) The posterior commissure (commissura posterior). 



When two pineal organs are present in or near the median plane, 

 the term " Epiphysis I " has been used to denote the more anterior and 

 " Epiphysis II " to denote the more posterior organ. When the term 

 " epiphysis " is used alone it is generally applied to the primary embryonic 

 diverticulum or to the pineal gland as distinct from the pineal eye or 

 parietal organ. Thus the name " epiphysis " is usually applied to the 

 deeply situated solid organ, e.g. that of the mammalian brain as contrasted 

 with the superficial sensory vesicle or pineal eye of the lamprey or 

 Sphenodon. 



In addition to the above-mentioned structures, which are included 

 in the parietal region of the brain, are accessory parts which comprise : 



The fibrous coverings or capsule. 



Pigment — (a) mesodermal ; (b) epidermal. 



Pineal vessels and nerves. 



The parietal cornea (Studnicka). 



The parietal plug (Dendy). 



The parietal spot (P. fleck). 



The parietal scale (P. schuppe). 



The parietal plate or pineal plate. 



The parietal pit or impression. 



The pineal- or parietal-foramen. 



The meaning of most of these terms is self-evident. The parietal 

 cornea is, however, defined by Studnicka as including all the translucent 

 tissues lying over the parietal organ and between it and the superficial 

 surface of the epidermis, whereas the name " parietal plug " was applied 

 by Dendy to the conical mass of transparent tissue between the lens of the 

 parietal organ and the deep surface of the corium or dermis in Geotria. 

 The terms pineal plate or parietal plate are given to the bony plate which 

 sometimes overlies the pineal organ in certain fishes and reptiles. The 

 pineal plate may lie between the frontals, between the frontal and parietal 

 bones, or between the parietal bones. It may or may not be perforated 

 by a parietal foramen. It is perforated in the skull of Lacerta agilis ; 

 not perforated in the arthrodiran fish Dinichthys intermedins found in the 



