loo BIOLOGY OF THE LABORATORY MOUSE 



According to Severinghaus (86) there is strong evidence that the chro- 

 mophobic cells are progenitors of distinct and divergent chromophilic cell 

 types, and that no transition between the basophils and acidophils is possi- 

 ble. The study of castrate pituitaries indicates that the chromophils may 

 revert to their chromophobic form. 



The pars intermedia is above the cleft and is in close contact with the 

 pars nervosa. It is very well developed in the mouse. The epithelial cells 

 are arranged in small irregular groups. Most numerous are the polygonal 

 cells with oval nuclei and non-granular cytoplasm. These are similar to the 

 chromophobe cells of the pars distalis. Spindle-shaped cells often as long as 

 the width of the pars intermedia are also present. They have dark staining 

 oval nuclei. These cells are considered by Benda (in Jaffe, 56) as endo- 

 thelial cells lining very minute capillaries. More general opinion maintains 

 that the intermedia has poor blood supply. 



The pars nervosa contains ependymal and glia cells and fibers. Elements 

 from the pars intermedia may project into this zone. Gersh (38) describes 

 specific parenchymatous cells which are distinguished from the neuroglia 

 cells elsewhere in the central nervous system by their characteristic cyto- 

 plasmic inclusions. In the mouse these cells have an oval nucleus and a 

 large prominent nucleolus. The cytoplasm contains osmophilic granules. 

 In other cells osmophilic granules are not present, but the cytoplasm is filled 

 instead by delicate basophilic granules which may be arranged in short 

 chains or clumped masses. Some cells are intermediate between these two 

 types. Gersh states that the parenchymatous glandular elements of the 

 neuro-hypophysis produce and secrete the antidiuritic substance. 



Thyroid gland. — The lateral lobes of the thyroid are situated on the 

 sides of the trachea, just below the larynx. They are connected by a very 

 narrow transverse lobe, the isthmus. The lobes are surrounded by a fibrous 

 capsule. The organ is composed of follicles of varying size which are 

 filled with colloid (Fig. 42). In section this material is homogeneous and 

 stains well with acid dyes. The follicles are lined by simple cuboidal epi- 

 thelial cells, having large, spherical, central nuclei and clear cytoplasm. 

 Occasionally round droplets of colloid or clear vacuoles may be present in 

 the cytoplasm. The cell outHnes are distinct. It is considered that glands 

 composed of tall cells are more active than those composed of low cells. 

 The follicular epithelium is surrounded by the interfollicular reticular con- 

 nective tissue, which is very rich in blood and lymph supply. 



Parathyroid glands. — Each parathyroid gland is surrounded by and 

 separated from the thyroid by a connective tissue capsule (Fig. 42). The 



