108 BLOOD-GLANDS AND DUCTLESS GLANDS. 



The lymphatics are also abundant, and through them the 

 secretion of the gland is probably removed. 



The function of the thyroid, as indicated by its rich blood- 

 supply and by the serious consequences of loss of the organ, 

 is of great importance. Its secretion is entirely " internal/' 

 and by its action metabolism and cell-life are stimulated and 

 hastened, obesity diminished, circulation is affected, and the 

 cerebrum stimulated. 



The parathyroids are small oval ductless glands about 6 to 

 10 mm. long, situated near the thyroid, usually two on each 

 side. They are enveloped by delicate fibrous tissue, and the 

 epithelial columns and alveoli are separated by delicate tra- 

 beculaB of similar tissue. The connective tissue is very vascu- 

 lar. The parenchyma of the parathyroid bodies consists of 

 polyhedral glandular epithelium-cells arranged in branching 

 solid columns or hollow tubes, some of which occasionally 

 contain secreted colloid material. The epithelium consists 

 mainly of clear cells with large nuclei, not dissimilar to the 

 cells of the thyroid gland. A few of the epithelial alveoli, 

 however, consist of larger cells with granular oxyphile bodies, 

 which look much like liver-cells ; these cells are altogether 

 different from those in the thyroid, and would seem to estab- 

 lish the individuality of the parathyroids as structures inde- 

 pendent and distinct from the thyroid. 



Little has yet been definitely ascertained as to the functions 

 of the parathyroids, nor their genetic or vicarious relations to 

 the thyroid. 



The Adrenal or Suprarenal Glands. 



General structure : These are ductless bodies made up of 

 columns and" masses of epithelium supported in sustentacular 

 tissue, and abundantly supplied with bloodvessels and nerves 

 (Fig. 45). The substance of the gland exhibits two parts, 

 the cortex or peripheral portion, and the medulla or central 

 portion. 



The sustentacular connective tissue consists of a fibrous 

 capsule enveloping the gland, and more delicate connective 

 tissue permeating the interior and lying between the epithelial 

 masses and vessels. 



