344 



THE DUCTLESS GLANDS 



with, and separated from one another by, the true anterior 

 lobe (Herring). 



The nervous part of the cod's pituitary is small, and appears 

 to be composed of neuroglia and ependyma cells, without 

 any true nerve cells. It is continuous with the brain in 

 front by the lamina post-optica, or anterior lamina, and at 

 the sides by lateral laminse. The nervous substance is more 

 freely invaded by cells of the pars intermedia than is the 

 nervous substance of the mammalian body. 



In Elasmobranchs (Raja batis) the pituitary is a long, 

 club-shaped body which lies for the most part behind the 

 small lobi inferiores. Its structure is very different from 

 that of mammals, birds, and Teleosts. There are no cells 

 having the deeply staining characteristic of those of the 

 anterior lobe of other vertebrates, and there are no cells 

 exactly like those of the pars intermedia. There is no differ- 

 entiation into anterior and posterior lobes, and the only trace 

 of a posterior lobe is a thin lamina of nervous tissue which 

 bounds the infundibular cavity. The saccus vasculosus is 

 well developed. The Elasmobranch pituitary appears to be 

 quite different from that of other vertebrates. 



B. Development of the Pituitary Body 



The earlier observers believed that the whole of the pituitary 

 body is derived from the brain. Rathke, however, described 

 the invagination of mucous membrane, since called " Bathke's 

 pouch," and put forward the view that from this pouch is 

 derived the epithelial portion of the pituitary (which he further 

 stated has been derived from the entoderm of the fore -gut). 



Dursy described the origin of the epithelial part from the 

 fore-gut, and of the vascular stroma from the notochord. 

 W. Muller showed that the anterior lobe arises from Rathke's 

 pouch, but believed this to be entodermal. It is now usually 

 considered that the pouch is of ectodermic origin. 



The posterior lobe was originally conceived as the anterior 

 extremity of the brain, but more recent researches have shown 

 that it is an outgrowth of the thalamencephalon. 



Mihalkovics has given a complete account of the early de- 

 velopment of the pituitary body in the rabbit and the chick. 

 According to this author, the anterior lobe is developed from 



