Histological Appeai-ances of the Maninialian Pituitary Body 147 



nm with the other longitudinal fibres in the inner layer. Similar appear- 

 ances were described by Berkley, but it is almost impossible to decide 

 whether longitudinal hbres arise from these cells or not ; they may be fibres 

 horn cells further back, which cross the cell processes in this situation. 



The layers of the neck of the infundibulum have been described by 

 several authors. Mihalkovics (25) noted them in the developing pituitary, 

 but believed that the inner layer is composed of connective tissue fibres, 

 arising from cells which enter the posterior lobe with the blood-vessels. 

 Lothringer (22) described them, and stated that the layers are prolonga- 

 tions of the tissue of the tuber cinereum into the posterior lobe, neuroglia 

 fibres increasing and nervous elements diminishing from before backwards. 

 According to Lothringer, the longitudinal fibres have their origin in the 

 tuber cinereum. This view has been adopted by most subsequent authors 

 except Berkley, who, on the other hand, regards them as nerve fibres 

 arising from cells in the posterior lobe, and passing upwards and forwards 

 to the brain. Cajal (quoted from Kolliker's " Gewebelehre," Bd. ii., 

 S. 604, 1896) found in two-days-old mice nerve fibres originating in the 

 tuber cinereum, and passing downwards into the body of the posterior lobe. 

 In the lobe itself he described one of the thickest plexuses of nerve fibres 

 known, and cells of a doubtful nature. 



The fibres are not medullated nerve fibres, and do not stain as such with 

 osmic acid in fresh teased preparations. They are much thicker than 

 ordinary non-medullated fibres, and are devoid of nuclei along their course. 

 Many of them resemble white fibrous tissue, but they are stained by Cajal's 

 method, although not so deeply as the nerve fibres in the adjacent brain 

 substance. The posterior lobe of the pituitary body of the cat, owing to 

 the persistence throughout life of its original cavity, is a particularly good 

 subject for the elucidation of the question of the origin of these longitudi- 

 nally running fibres. In this animal the fibres clearly arise from cells lining 

 the cavity of the body and neck, and pass forwards and upwards towards 

 the brain. They are the fibres of ependyma cells. After a course of varying 

 length, they break up into fine fibrils which enter the outer layer and ter- 

 minate on its external surface. The origin of the fibres can be traced in the 

 developing organ, and their elongation and oblique course explained. The 

 cell bodies, from which the fibres proceed, move downwards and backwards 

 with the growth of the infundibulum, but the outer ends of the fibres remain 

 attached to the junction with the epithelial part, and do not participate in 

 the movement. New fibres arise during growth, some of them apparently 

 taking origin from cells which lie deeper and not lining the cavity. In the 

 front portion of the anterior lamina most of the ependyma fibres run verti- 

 cally, and have only a very short course (fig. 13). There are numerous cells 

 in the tuber cinereum, and fibres pass into or out of this body ; it is difficult 

 to tell where their cells of origin lie. Some fibres may arise in the tuber 

 cinereum, but they resemble the ependyma fibres, and probably belong to 

 ependyma or neuroglia cells. 



