THE THYROID AND PARATHYROIDS 269 



to resemble the other Herbivora in the distribution of its para- 

 thyroids. 



(/) In Sheep and Goats there are two parathyroids embedded 

 more or less in the thymus, and two others in the substance of 

 the thyroid. The thyroid of the sheep varies extremely in 

 size in different individuals. 



C. Histology of the Thyroid in Man and Mammals 



The larger lobes of the thyroid are surrounded by a thin 

 capsule of connective tissue, and are divided, by processes 



k^tf^-d >w " x 



\ 



e. ves. 



' interves. 



FIG. 77. Thyroid of normal dog. (X 120.) 



c., colloid ; e, ves., epithelium lining vesicles ; e. interves., ephitelial intervesi- 

 cular tissue ; c. ves., colloid vesicles. 



running into the interior of the organ, into smaller and smaller 

 lobules. The ultimate lobules are of irregular form and size, 

 but are, for the most part, roughly circular or oval in section, 

 and have a diameter of about 0-5 to 1-0 millimetres. The 

 interior is mostly occupied by vesicles of varying size, 45 /^ to 

 110 //, and varying shape. It was formerly thought that the 

 gland was made up of a system of branching alveolated canals, 

 but it has been conclusively shown that the glandular substance 

 is composed of closed vesicles, which are separated from one 

 another by fine strands of connective tissue, and a variable 

 amount of an inter vesicular cellular tissue. Most of these 



