15() Herring 



which liave been so frequently recorded at some time or other in the 

 history of cases of acromegaly and of affections and lesions associated 

 with the base of tlie skull. 



Summary. 



Three types of mammalian pituitary body are recognised. In one, e.g., 

 the cat, the posterior lobe is hollow and its cavity is in free communication 

 with the third ventricle of the brain, while the epithelium of the anterior 

 lobe affords an almost complete 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 communicates with the third ventricle : the posterior 

 lobe is here again almost completely surrounded with epithelium ; 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 two 

 distinct parts : an anterior lobe proper, consisting of solid columns of cells, 

 between which run wide and thin- walled blood-channels ; and an inter- 

 mediate 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 proto- 

 plasm 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 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 (Berkley). 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 region of the neck, and 

 islets of these cells are frequently found throughout the posterior lobe ; 



