The Development of the Mammalian Pituitary Body 173 



Gaupp found large blood-spaces of a venous nature, and states that the 

 epithelium grows into them, passing through their walls. Mi not also 

 inferred from the structure of the anterior lobe of the pituitary that the 

 development of its blood-vessels is partly sinusoidal. While the anterior lobe 

 and tongue-like process of epithelium are extremely vascular, that part of 

 the wall of the original sac which is applied to the brain remains devoid of 

 blood-vessels. Its cells proliferate and spread round the nervous substance 

 of the posterior lobe, forming a covering of epithelium of varying thickness. 

 The nervous portion of the posterior lobe has meanwhile grown in length 

 and expanded to form a definite body, which, in the cat, retains a large 

 central cavity. The neck is constricted, but remains hollow. In a 35-mm. 

 cat embryo (fig. 5) the epithelium lining the central cavity is composed of 

 ependyma cells with thin processes, the nervous tissue is small in amount, 

 contains few cells, and is chiefly made up of the processes of the lining 

 cells. At the postero-superior angle of the lobe there is frequently seen a 

 knob-shaped body (n) of large and deeply staining ependyma cells, behind 

 which are blood-vessels. This vascular knob appears to be growing into 

 the central cavity, and marks the entry of blood-vessels into the posterior 

 lobe. The thickening of epithelium does not persist, but disappears ; the 

 blood-vessels, however, grov^^ into the lobe in this situation. The appear- 

 ance is not a constant one, but when it occurs the deeper staining of the 

 ependyma cells and the vascularity of the tissue behind them are striking 

 features. The blood-vessels of the posterior lobe of the pituitary are, in 

 the cat, almost entirely derived from an ingi-owth in this situation ; true 

 capillaries are formed in the lobe and are accompanied by a small amount 

 of connective tissue. The latter is nev^er present in large quantities, and 

 the posterior lobe of the pituitary does not become a connective tissue 

 appendage of the brain, as stated by W. Miiller and many others; there 

 is remarkably little connective tissue in the posterior lobe. The appear- 

 ance which W. Miiller likened to a spindle-celled sarcoma is very marked 

 in the older pituitary. It is, however, not due to the presence of connective 

 tissue fibres and cells, for when the pituitary is prepared b}^ Cajal's silver 

 method it is found that the appearances described by W. Miiller are caused 

 by the presence of large numbers of ependyma- and neuroglia-cells and 

 fibres, chiefly the former. In the developing pituitary there is never any 

 sign of true nerve cells. The ependyma cells lining its central cavity are 

 at first like those lining the third ventricle of the brain. Their fibres 

 run vertically and end at the outer surface of the lobe. As the posterior 

 lobe elongates the peripheral ends of the fibres remain attached, the cells 

 become more numerous, and are moved fui'ther and further from the points 

 of attachment of their fibres. In this way the ependyma fibres of the neck 

 of the posterior lobe acquire an oblique direction, and finally run almost 

 longitudinally, their cells of origin being situated much further back than 

 the outer ends of their fibres. In the posterior lobe of the kitten, especiallv 

 in the region of the neck, the ependyma fibres become very numerous, and 



