ADULT PINEAL ORGAN OF BIRDS 



295 



hemispheres ; and in young birds the cavity, which is lined by columnar 

 ependymal cells, communicates with the third ventricle. No nerve- 

 fibres are present either in the stalk or external to it. 



The second type of tubular epiphysis with thick walls (Fig. 202) occurs 

 in the grosbeak, which is allied to the finches. The organ is a thick- walled 

 tube ending blindly beneath the roof of the skull. It is somewhat lobu- 

 lated, and in the adult animal is frequently separated from its original 

 connection with the roof of the brain, its narrow stalk having been rup- 

 tured. Its lumen is lined by ependymal epithelium and sends tubular 

 diverticula into the substance of the wail, but there is no true formation 

 of follicles. 



CbK 



Fig. 202. — Sagittal Section through the Cerebellum and Epiphysis of a 



Grosbeak, Coccothraustis vulgaris. (After Reichert.) 



Cbl. : cerebellum. Ep. : epiphysis. 



2. The follicular type of epiphysis is the most common. It consists 

 of a mass of completely separated hollow follicles and short tubes which 

 have originated as outgrowths from the original embryonic diverticulum 

 from which they have subsequently been cut off as independent vesicles. 

 Even in the adult some follicles may still retain their primary connection 

 with the central lumen or one of its branches. A vascular connective 

 tissue is interposed between the follicles, which is continuous externally 

 with a thin fibrous capsule. There is a rich vascular supply, but, as in 

 the other types, no nerves connecting the epiphysis with the central 

 nervous system are present. 



3. The solid lobular type (Fig. 203). The organ consists of a con- 

 glomeration of solid lobules held together by thin fibrous septa. The 

 cavities of the lobules are either partially or completely obliterated, and 



