THE PITUITARY BODY. 



309 



The significance of the pineal body in man, long an unsolved riddle, has 

 been shown by embryological and comparative studies of the organ in the 

 lower vertebrates, especially in lizards, to be that of a very imperfectly 

 developed and greatly modified rudimentary sense-organ. In certain 

 lizards, in which it reaches a high development, the pineal body is a flat- 

 tened cup-shaped organ (Fig. 355) connected with the brain by a stalk 

 containing nerve-fibres. The structural resemblance to an invertebrate 

 visual organ, a sort of lens overlying a retina-like layer, suggested a possible 

 similarity of purpose in the higher types. The organ was designated, there- 

 fore, the pineal eye, although probably in no existing animal a functioning 

 structure. The embryonic relations in many reptiles are most suggestive of 

 the significance of the pineal body as a rudimentary sense-organ, although not 

 necessarily an eye. 



THE PITUITARY BODY. 



The pituitary body, or hypophysis cerebri, is attached to the dependent 

 tip of the infundibulum, the narrow funnel-like projection from the floor of 

 the third ventricle. It is of flattened oval form, somewhat mushroom- 

 shaped, and measures about 12 mm. in the transverse and about 7 mm. in 

 the sagittal diameter. The pituitary body includes two entirely distinct 

 parts, the anterior and posterior lobes, which differ both in origin and struct- 



Pars intermedia 



Posterior or cerebral lobe 



.-space 



Connective tissue 

 trabecula 



Capsule 



FIG. 356. Horizontal section of pituitary body, showing relation of anterior (oral) and posterior 



(cerebral) lobes. X 7. 



ure. The former is derived as an outgrowth from the roof of the primitive 

 oral cavity, while the latter is developed as a tubular evagination from the 

 floor of the second brain-vesicle, the diencephalon. 



The Anterior Lobe. The anterior and glandular division, which 

 constitutes the major part of the hypophysis, is surrounded by a robust 

 fibrous capsule that is continuous with the thinner investment enclosing the 

 posterior lobe. From the deeper surface of the capsule, as well as from a 

 condensation of connective tissue on each side of the mid-line that marks the 

 position of large blood-vessels, fine processes extend inwards and form a deli- 

 cate supporting fibrous reticulum, rich in capillaries, whose meshes are filled 

 with spherical or cord-like masses of cuboidal or polygonal epithelial cells. 

 The latter are principally of two kinds the smaller chief cells (30-40 ju), 



