800 THE THYROID BODY. [BOOK n. 



which has followed not only the subcutaneous injection of but 

 even mere feeding with, the extract of fresh thyroid ; the effective 

 substance, the precise nature of which has not yet been made out, 

 is not injured in the process of digestion though it may be 

 destroyed by boiling. We may add that the condition of ' creti- 

 nism,' which has many analogies with the failure of the nervous 

 system and apathy spoken of above as resulting from the removal 

 of the thyroid in animals, has long been known to be associated 

 with disease of the thyroid (goitre). 



The large vascular supply of the thyroid and the phenomena 

 of a disease known as exophthalmic goitre, in which vascular en- 

 largement of the thyroid is associated with cardiac symptoms and 

 other vascular disturbances, especially of the head, have suggested 

 that, apart from metabolic processes, the circulation in the thyroid 

 may, perhaps in a more or less mechanical way, be connected with 

 and influence the circulation in the brain. But the exact nature 

 of this influence has not been made clear. 



496. The Pituitary Body. The lower, posterior, lobe of this 

 organ resembles the thyroid body (the upper, anterior, lobe is 

 of quite distinct nature, being really a part of the central nervous 

 system) in as much as it is a diverticulum of the alimentary canal 

 (namely of the mouth), which instead of becoming a branched 

 gland is converted into a mass of round, or oval, or cylindrical 

 alveoli separated by septa of vascular connective tissue. Though 

 in some instances the alveoli of the pituitary body like those of 

 the thyroid possess a lumen, which moreover may hold more or 

 less ' colloid ' contents, the majority are solid masses of epithelial 

 cells. The cells, which are columnar or polyhedral, present no 

 special characters, except perhaps that between the usual epi- 

 thelial cells are occasionally found spindle-shaped cells, apparently 

 of mesoblastic origin. 



Concerning the processes which take place in these alveoli and 

 the purposes of the organ as a whole we know absolutely nothing. 



497. The Suprarenal Bodies. A (mammalian) suprarenal 

 body when cut across is seen to consist of two distinct parts, an 

 outer thicker cortical part, of yellowish colour, striated radially, 

 and an inner thinner medullary part of darker colour. At the 

 depression on the anterior surface called the hilus, whence issues 

 the comparatively large suprarenal vein, the cortex thins away so 

 that the medulla comes to the surface. These two parts, cortex 

 and medulla, are not, like the cortex and medulla of a lymphatic 

 gland, different arrangements of the same material, but are of 

 essentially different nature and indeed are of different origin. 

 The medulla is derived from, is a modification of, sympathetic 

 ganglia, while the cortex is derived from masses of mesoblastic 

 cells surrounding the great blood vessels ; and in some' animals 

 the two form wholly separate bodies. The so-called accessory 

 suprarenal bodies are composed of cortex alone. 



