Histological Appearances of the Maimualiaii Pituitary Body 139 



usually well defined by the occurrence of coarsely granular cells in the 

 latter. The cells of this part are very like the clear cells of the anterior 

 lobe, and are closely packed together in solid columns ; occasionally they 

 spread downwards a little over the front of the anterior lobe (see fig. 2). 

 Behind they are continuous with the epithelial covering of the posterior 

 lobe, the cells of which they closely resemble. 



The epithelial covering of the posterior lobe was described by 

 Peremeschko (30), who gave it the name of " Markschicht." He found 

 it to vary in thickness in different situations, and to be firmly attached 

 to the nervous substance. He also noted the presence of colloid vesicles 

 in the " Markschicht " of the dog's pituitary, and that the cells are unlike 

 those of the " Korkschicht " or anterior lobe. Lothringer (22) gave 

 it the name of " Epithelsaum," a term which is used by Retzius (33) and 

 later observers. Peremeschko was the first to point out that the cleft 

 lies in the part of the pituitary which is composed of epithelium, and 

 that it does not separate epithelial from tissue of nervous origin, as had 

 previously been thought. In addition to the ordinary epithelial cells 

 which are found in the "Epithelsaum," Lothringer described marginal 

 cells which lie between the others and reach the free border, or are 

 arched back upon themselves. Similar cells have been figured by 

 Retzius (33) in Golgi preparations, and compared by him to neuroglia 

 cells. According to Retzius they are, for the most part, small and 

 thread-like, and reach through the whole border. Other cells do not 

 pass right through, but are branched. The cell nuclei are often placed 

 near the outer end, while the inner end widens to a three-cornered foot, 

 which is placed against the nervous tissue of the posterior lobe. The 

 structure of the epithelial border is shown in fig. 9, which is taken from 

 a section of kitten's pituitary prepared by Cajal's silver method. Long, 

 thin nucleated cells of a spindle shape are numerous, and take a vertical 

 course through the epithelium. They appear to be of ectodermic origin, 

 and act as supporting cells. Similar cells are found in the adult, but are 

 better seen in the young animal. A section through the epithelial 

 covering of the adult pituitary gives appearances shown in fig. 6. The 

 cells are arranged in several layers over the greater part of the body 

 of the posterior lobe, but are much thicker in some places than in others. 

 In the cat a great accumulation of epithelial cells is found in the region 

 of the lower part of the neck of the infundibulum, forming a thick mass 

 between the cleft and nervous substance. Colloid material may be present 

 in rounded spaces between adjacent cells in any part of the covering, but 

 the vesicles are largest and most numerous in the thicker parts round the 

 neck. In some cats there is a great development of the epithelium at the 

 sides of the posterior extremity of the nervous lobe. In this situation there 

 are distinct tubules which open into the cleft. The cells forming the walls 

 of the tubules are clear and devoid of granules, and there is an absence 

 of colloid material. This tubular arrangement is not always present. 



