l8o8 



HUMAN ANATOMY. 



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

 media. They are of moderate size and lined with cuboidal epithelium, and usually 

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

 rior lobe (SchoenemannJ. 



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 



Wall of rhombencephalon 



ituitary evagiiiatlon from diencephalon 



Pituitary evagination from oral cavity 



Communication with oral 

 cavity 



Wall of 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 

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

 needs further confirmation, since, as pointed out by Thom,' 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 



Fii^- 1533- 



Cerebral evagination 



VVall of diencephalon 



cavity of the interbrain 

 (diencephalon), the an- 

 terior lobe is derived 

 from an ectoblastic 

 outgrowth from the pri- 

 mary oral ca\ity which 

 appears during the 

 fourth week. The cere- 

 bral end of this evagina- 

 tion ( Ratlike s pouch ) 

 soon expands into the 

 hypophysial 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- 

 pophysial anlage then lying within the cranium against the lower surface of the 

 interbrain. In very exceptional cases a canal in the sphenoid bone, leading from 

 the sella turcica to the base of the skull, contains a jirolongation of the hypophysis, and 



* Archiv f. mikro. Anat., Rd. Ivii., 1901. 



Wall of 

 rhombencepbaUin 



Oral evaginatioti 



Portion of sagittal section of rabbit embryo, showing development of 

 pituitary body. K 80. 



