Histological Appearances of tlie Mammalian Pituitary Body 155 



vessels. The posterior lobe is supplied by a median artery which enters it 

 at its postero-superior extremity ; branches run forwards near the central 

 cavity, and break up into capillaries. The veins of the posterior lobe are 

 situated immediately beneath the epithelial investment, and converge 

 towards the place of entrance of the artery ; leaving the lobe in this situation, 

 they turn outwards to join the large lateral sinus on either side. Some of 

 the veins from the anterior lobe appear to take a similar course, passing 

 through the epithelial investment of the neck of the infundibulum to run 

 in the nervous portion ; others leave the anterior lobe at its neck and pass 

 outwards into the lateral sinus. The presence of so many large arteries 

 and veins in the immediate vicinity of the pituitary body would render the 

 operation of removing it an extremely difficult one, even were the organ so 

 situated as to be convenient of access. Mi not (26) states that the blood- 

 vessels of the anterior lobe of the pituitary will probably be found to have 

 a sinusoidal development. This appears to be partly true at any rate of 

 the anterior lobe of the pig's pituitary. 



COXCLUSIOXS. 



We may conclude from the histological appearances of the mammalian 

 pituitary body that it is an organ of physiological importance It may be 

 divided into two parts, which show structural differences probably indicative 

 of distinct functions. 



The anterior lobe, consisting of large granular cells and numerous blood- 

 vessels, is a gland producing an internal secretion which is poured directly 

 into the blood. It is a blood-vascular gland, the function of which is 

 undetermined, but which may exercise an influence on growth. The care- 

 ful examination of the pituitary body in cases of acromegaly ma}' tiirow 

 some light upon this question ; at present any statement as to its probable 

 functions must be purely speculative. 



The posterior lobe is made up of two structures. Of these, the part 

 developed from the brain and consisting of neuroglia and ependyma cells 

 and fibres acts as a framework. It is more or less surrounded and invaded 

 by epithelium, which probably furnishes its active part. There is histologi- 

 cal evidence of a secretion produced by the epithelial cells, which apparently 

 passes into lymph- vessels, and is destined to enter the ventricles of the brain 

 The posterior lobe of the mammalian pituitar}^ is a brain gland, not b\ 

 virtue of tissue of brain origin, but by the growth into it of epithelial cells 

 of ectodermic origin. Extracts have the property of producing marked 

 effects on cardiac and plain muscle fibres comparable in some respects to 

 the action of the medulla of the suprarenal capsule. They have also a 

 selective action upon the kidney, causing dilatation of the renal blood- 

 vessels and diuresis. Disturbances of the posterior lobe of the pituitary 

 are probabl}'' responsible for the occurrence of the diabetic conditions 



