386 THE DUCTLESS GLANDS 



sac-like structure, which subsequently becomes lobed and 

 solid. This is the pineal body. The proximal part of the 

 evagination remains hollow, and forms the pineal stalk, and the 

 whole structure, body and stalk, is usually called the epipliysis 

 (McMurrich). 



In the Reptilia and other lower groups of animals the out- 

 growth from the roof of the diencephalon is double, a secondary 

 outgrowth arising from the base or from the anterior wall of 

 the primary one. This secondary outgrowth the anterior 

 evagination becomes elongated until it reaches the epidermis 

 of the head, and here it develops into the pineal eye. In 

 mammals this anterior process is not developed. 



In addition to the epiphysial evagination another evagination 

 arises from the roof -plate of the first cerebral vesicle. This is 

 placed farther forward in the region which subsequently 

 becomes the median portion of the telencephalon. This 

 structure is called the par&phyeig, and is found in the lower 

 vertebrates and in the marsupials (Selenka), but up to the 

 present time has not been found in other groups of the Mam- 

 malia. It is supposed to be comparable to a choroid plexus 

 which is evaginated from the brain surface instead of being 

 invaginated, as is usually the case. There is no evidence 

 that a paraphysis is developed in the human brain (McMurrich). 



Histological Structure of the Pineal Body 



The pineal body is covered on its upper surface by the pia 

 mater, which provides the connective-tissue skeleton of the 

 organ, and carries the bloodvessels into the interior. This 

 sheath of connective tissue sends in septa, which break up 

 into a fine network in the parenchyma of the gland, and divide 

 up the whole structure into "acini," or "follicles." (Figs. 104 

 and 105.) 



Some writers state that there are no true septa, but irregular 

 trabeculse. It seems that in regard to the distribution of the 

 connective-tissue frame-work of the pineal body there is 

 considerable difference between different species and between 

 different animals of the same species, but of different ages. In 

 the connective-tissue cells a yellowish or brownish pigment is 

 frequently found. 



A number of cross -striated muscle fibres may be found in 





