ORGANS OF THE BODY. 



441 



The thyroid gland is found to "be made up of closed vesicles of roundish 

 form embedded in vascular connective -tissue (fig. 425, a, b). These 

 appear, at first sight, like closely grouped granules of 0'5641-1'1279 mm. 

 in diameter, rounded or flat, and of a reddish-yellow colour. They are 



Fig. 425. Two lobules from the thyroid of a a infant. 

 a, small glandular vesicles and their cells; 6, the 

 same with incipient colloid metamorphosis more 

 strongly marked at c; d, coarse lymph canals; and 

 e, fine radicals of the same ; /, an efferent vessel of 

 considerable size. 



Fig. 426. Colloid metamorphosis. 

 a, glandular vesicle from the 

 rabbit; if incipient colloid me- 

 tamorphosis from the calf. 



again arranged in small lobules, and these in larger lobes, the considera- 

 tion of which we leave for descriptive anatomy. 



The stroma is made up of ordinary fibrillated connective-tissue of toler- 

 ably loose texture, mixed with elastic elements. The gland vesicles, 

 0'0501-0'1026 mm. in diameter, possess a limiting membrane formed of 

 rather delicate homogeneous connective-tissue, which is enveloped exter- 

 nally in a dense round network of capillaries. The latter of a diameter of 

 about 0-0072-0-0115 mm. in the dog, and 0'0088-0'0115 and 0-0114 mm. 

 in the calf, are arranged in meshes of an average breadth of 0-0201-0-0226 

 mm. Their internal surface (fig. 426, a, b) is clothed with low cylin- 

 drical cells about 0-0196 mm. in height and 0*0113 mm. in breadth. 

 These resemble epithelium, and contain nuclei of about 0*0086 in diameter 

 (Peremeschko). The cells separate very easily from the walls in conse- 

 quence of decomposition, and on their solution the nuclei become free. 

 In the embryo the cavity of the round gland capsule is represented at 

 first by a finely granular substance, in which cells and nuclei are 

 embedded. Later on the growing cavity is usually seen to contain a 

 homogeneous, transparent, and almost fluid substance, known as colloid 

 matter (p. 21). By it the whole interior of the gland capsule is com- 

 pletely filled in the fully developed animal. 



The recent researches of Frey and Peremescliko have made us 

 acquainted with the lymphatic vessels of the part. The whole envelope 

 of the organ is covered by knotted trunks, which take their origin from 

 a network of very complicated canals, situated in a deeper layer of the 

 former. This latter network is formed around the secondary lobules 

 of the gland by the reticular intercommunications of these canals (fig. 

 425. /). 



