ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 703 



rence of the diabetic conditions which hav r e been frequently recorded in 

 cases of acromegaly and of affections and lesions associated with the 

 base of the skull. 



Three types of Mammalian pituitary body are recognised. In one, 

 e.g. the cat, the posterior lobe is hollow and in free communication with 

 the third ventricle, while the epithelium of the anterior lobe forms an 

 investment for the posterior lobe. In the second type, e.g. the dog, the 

 body of the posterior lobe is solid, but the neck is hollow and commu- 

 nicates with the third ventricle, and the anterior lobe again forms an 

 investment. In the third type, e.g. man, monkey, ox, pig, and rabbit, 

 the body and neck of the posterior lobe are solid, although traces of a 

 cavity are occasionally found in the neck ; in this type the epithelium 

 does not invest the posterior lobe so completely, but is aggregated 

 around the neck and spreads over and into the adjacent surface of the 

 brain. 



The epithelial portion of the pituitary body is differentiated into (a) 

 an anterior lobe proper, consisting of solid columns of cells, between 

 which run wide and thin-walled blood-channels ; and (b) an intermediate 

 portion, which lies between the anterior lobe and the nervous tissue of 

 the pituitary, forming a closely fitting investment of the latter. 



The anterior lobe contains cells which are clear or hold in their 

 protoplasm varying amounts of deeply staining granules. They are 

 probably different functional stages of one and the same kind of cell, 

 and the granules give rise to a secretion which is absorbed by the blood- 

 vessels. 



The intermediate portion consists of finely granular cells, arranged 

 in layers of varying thickness closely applied to the body and neck of 

 the posterior lobe and to the under surface of the adjacent parts of the 

 brain. The part of it which is separated from the anterior lobe by the 

 cleft is almost devoid of blood-vessels. In the cat the portion lying in 

 front of the anterior lobe has a tubular appearance, and is very vascular. 

 Colloid material occurs between the cells of the pars intermedia, and in 

 most situations appears to pass into the adjacent nervous substance, to 

 be absorbed by blood-vessels or lymphatics. 



The nervous portion of the pituitary body is made up of neuroglia 

 cells and fibres. Ependyma cells line the central cavity in the cat and 

 send long fibres forwards and upwards towards the brain, most of which 

 terminate in the outer part of the neck. There are no true nerve-cells, 

 and the nerves supplying the pituitary probably reach it through 

 sympathetic fibres accompanying the blood-vessels (Berkeley.) The 

 nervous portion is invaded to a large extent by the epithelial cells of the 

 pars intermedia. Columns of epithelial cells grow into it, especially in 

 the neck, and islets of these cells occur frequently throughout the 

 posterior lobe. In the pituitary of the cat, epithelial cells may even 

 grow into its central cavity. 



A substance histologically resembling the colloid of the thyroid 

 gland, but probably of a different nature, occurs in large quantity in the 

 nervous portion of the posterior lobe. It appears to be a product of the 

 epithelial cells, and, in the cat at any rate, to be carried by lymphatics 

 into the central cavity, and so into the third ventricle of the brain. In 



