THE PINEAL BODY 17 



4. THE COMPARATIVE MORPHOLOGY OF THE PINEAL REGION 



To make the proper evaluation of the pineal body this organ 

 should be considered in relation to its immediate encephalic 

 environment. Indeed, any study of the pineal organ which 

 omitted this environment would give but an inadequate view of 

 the epiphysis. A number of structures make their appearance 

 in connection with the roof-plate of the forebrain. Some of these 

 have a marked constancy; some are transitory, making their 

 appearance in one or two classes of vertebrates only, yet all of 

 them have a definite, phylogenetic significance in connection 

 with the epiphyseal complex. Embryologically, the roof-plate 

 of the primitive forebrain vesicle, that is, the prosencephalon, 

 gives rise to a number of evaginations. Certain of these even- 

 tually become prominent, adult organs. The most conspicuous, 

 both because of its constancy throughout the phylum and 

 its numerous adaptations, is the pineal or epiphyseal complex. 

 It has been suggested that the structures which form the roof 

 of the interbrain be known collectively as the pineal region. 

 This suggestion made by Minot ('Ol) 277 offers a convenient term 

 for the identification of a complex area of the brain. According 

 to Minot, the pineal region begins at the lamina terminalis or 

 lamina neuroporica which is its cephalic limit and comprises the 

 following elements: 



1. The paraphyseal arch. 



2. The velum transversum. 



3. The post velar arch, also known as the dorsal sac. 



4. The epiphysis, also known as the corpus pineale. 



5. The posterior commissure. 



Minot's specification of the pineal region needs some extension 

 in order to meet the requirements of all classes of vertebrates. 

 The following description of the pineal region makes provision 

 for all of the elements which may and in some instances do 

 appear in this area of the brain. 



Paraphysis. The paraphysis is an evagination situated at 

 the extreme cephalic end of the forebrain roof-plate. Ventrally 

 it is continued into the lamina neuroporica. Dorsally it is con- 

 tinuous with the velum transversum. Minot assumed that the 



MEMOIR 9 



