EPIPHYSIS AND HYPOPHYSIS. 423 



completely filled with cellular elements are found. Other follicles 

 contain peculiar concretions, known as brain-sand or acervulus, of 

 irregular round or oval or mulberry shape. Medullated nerve-fibers 

 have been traced into the epiphysis, but their mode of termination is 

 not known. 



The hypophysis, or pituitary body, consists of two lobes. The 

 posterior or infundibular lobe is developed from the floor of the first 

 primary brain-vesicle, and remains attached to the floor of the third 

 ventricle by a stalk, known as the infundibulum ; the anterior or 

 glandular lobe develops from a hollow protrusion derived from the 

 primary oral ectoderm. The distal end of this protrusion or pouch 

 comes in contact with the anterior surface of the lower portion of the 

 infundibulum, and becomes loosely attached to it. As the bones at 

 the base of the skull develop, the attenuated oral end of this pouch 

 atrophies, the distal end becoming finally completely severed from 

 the buccal cavity. " 



In the infundibular lobe of the hypophysis of the dog, Berkley 

 (94) described three portions presenting different microscopic struc- 

 ture. His account will here be followed : (i) An outer stratum 

 consisting of three or four layers of cells resembling ependymal 

 cells, which are separated into groups by thin strands of fibrous 

 tissue entering from the fibrous covering of this lobe. (2) A zone 

 consisting of glandular epithelial cells which in certain places are 

 arranged in the form of alveoli, often containing a colloid substance. 

 This zone merges into the central portion, (3), containing variously 

 shaped cells and connective-tissue partitions with blood-vessels. In 

 this portion neurogliar cells (see these) and nerve-cells were stained 

 by the chrome-silver method. 



The glandular or anterior lobe resembles slightly in structure 

 the parathyroid. This lobe is surrounded by a fibrous tissue capsule 

 and within it are found variously shaped alveoli or follicles, or, 

 again, columns or trabeculae of cells separated by a very vascular 

 connective tissue. In the alveoli or columns of cells are found two 

 varieties of glandular cells, which may be differentiated more by 

 their staining reaction than by their size and structure, although 

 they present slight structural differences. One variety of cells pos- 

 sesses a protoplasm which shows affinity for acid stains ; these are 

 known as chromophilic cells. They are of nearly round or oval 

 shape, with nuclei centrally placed, and have a protoplasm present- 

 ing coarse granules. The other variety of cells, known as chief 

 cells, are more numerous than the chromophilic. They are of cubic 

 or short columnar shape, with nuclei placed in the basal portions 

 of the cells and with protoplasm showing a fine granulation and 

 with an affinity for basic stains. Now and then alveoli containing 

 a colloid substance, similar to that found in the alveoli of the thy- 

 roid gland, may be observed. The blood-vessels of the glandular 

 portion are relatively large, the majority of them having only an 

 endothelial lining which comes in contact with the glandular cells. 



