I80 8 



HUMAN ANATOMY. 



ing acini lie chiefly against the posterior lobe in what has been termed the pars inter. 

 JV/. They are of moderate size and lined with cuboidal epithelium, and usua lly 

 normally present, although colloid vesicles may be absent in other parts of the ante- 

 rior lobe (Schoenemann). . ... 



The absence of excretory ducts, the activity of the epithelial cells as excretory 

 elements, and their intimate relation to the blood-vessels all support the view that 



FIG. 1532. 



Wall of rhombencephalon 





Pituitary evagination from diencephalon 



uitary evagination from oral cavity 



'".'ntvmuinication with oral 

 cavity 



Portion of sagittal section of rabbit embryo, showing early stage of development of pituitary body. X 80. 



the anterior pituitary lobe is to be regarded as an organ engaged in internal secre- 

 tion. Its assumed function as directly concerned with somatic growth, suggested by 

 tin- enlargement of the pituitary body observed in giants and in cases of acromegaly, 

 needs further confirmation, since, as pointed out by Thorn, 1 such changes are by no 

 means constant. 



Development. As above stated, the two lobes of the pituitary body are de- 

 veloped from entirely different sources. While the posterior lobe originates as a 



tubular extension of the 



FIG. 1533. cavity of the interbrain 



(diencephalon), the an- 

 terior lobe is derived 

 from an ectoblastic 

 outgrowth from the pri- 

 mary oral cavity which 

 appears during the 

 fourth week. The cere- 

 bral end of this evagina- 

 tion ( /w?///Xv'j pouch) 

 soon expands into the 

 hypophysis] pouch, 

 which remains con- 

 nected with the mouth 

 for a considerable time, 

 until the formation of 

 the base of the primi- 

 tive skull leads to sev- 

 erance of the tubular 

 communication, the hy- 



afflage then lying within the cranium against the lower surface of the 

 In verv exceptional cases .1 canal in the sphenoid bone, leading, from 

 (lie (MM .1 the skull, contains a prolongation of the hypophysis, and 

 1 Arrhiv f. mikro. Anal., IU1. Ivii., 1901. 



Cerebral evagination 



Wall of diencephalon 



Wall ..f 



< n. il < \ agination 



.!>t'tt iiihivn. -.liuvvitiK ilcvrli.pment of 



j Illlll.HS |i,,i| V . X 80. 



