THE THYEOID GLAND 451 



NERVES. The adrenal is well supplied with small sympa- 

 thetic nerve trunks; in fact, the ontogenetic relations between 

 the adrenal and the large sympathetic ganglia of the solar plexus 

 are extremely intimate, the cells of the medulla apparently taking 

 their origin, in embryos about 3 cm. in length, from the primitive 

 anlages of the sympathetic ganglia. 



The sympathetic nerves form a plexus in the capsule from 

 which branches are distributed to the cortex and to the medulla. 

 In the cortex they invest the blood vessels with a delicate plexus, 

 but have not been found within the epithelial cell columns. In 

 the medulla they are also distributed to the blood vessels and are 

 supplied with occasional small ganglia. From the plexus of sym- 

 pathetic nerve fibres which invests the groups of medullary epithe- 

 lium, Dogiel * demonstrated delicate fibrils, supplied with minute 

 varicosities, which penetrate between the epithelial cells and ter- 

 minate in a manner very similar to that which is characteristic of 

 the epithelial parenchyma of other secreting glands. 



II. THE THYKOID GLAND. 



The thyroid consists of a mass of glandular tubules or follicles, 

 supported by a connective tissue stroma and supplied with a thin 

 but dense fibrous capsule which closely invests the surface of each 

 of its lobes. 



The Connective Tissue Framework. The capsule of the thyroid 

 consists of dense white fibrous and elastic tissue, from which tra- 

 beculae, containing the larger blood vessels, pass inward and pro- 

 duce an indistinct lobular subdivision. A network of delicate 

 fibres, among which are very few if any elastic fibres, passes from 

 the trabeculae and invests the glandular follicles, forming a deli- 

 cate basement membrane for their epithelium. Flint f has shown 

 that much of this interf ollicular connective tissue is of the reticu- 

 lar variety. In it are contained the smaller blood vessels and 

 lymphatics. It also contains a few leucocytes, which are scattered 

 about in a diffuse manner. 



The follicles of the thyroid are ovoid saccules or short branched 

 tubules with frequent diverticula (Streiff {). They vary greatly 

 in diameter and in the calibre of their lumen. Many of them pre- 

 sent scarcely any lumen, others appear, from their extreme size 



* Arch. f. Anat., 1894. f Johns Hop. Hosp. Bull., 1903. 



J Arch. f. mik. Anat., 1897. 



