922 



THE THYROID BODY. 



a yellow fluid, with corpuscles resembling cell-nuclei and sometimes nu- 

 cleated cells floating in it. These vesicles are surrounded by capillary ves- 

 sels, and are held together in groups or imperfect lobules by areolar tissue. 

 Their size varies from ^-^th of an inch to that of a millet-seed, so as to be 

 visible to the naked eye, the size varying, however, in different individuals, 

 more than in the same thyroid body. The vesicles are spherical, oblong, or 

 flattened, and are perfectly distinct from each other ; the corpuscles within 

 them are in the foetus and young subject disposed in close apposition 

 and like a single epithelial layer on the inner side of the vesicles, but 

 for the most part detach themselves in the progress of growth. The fluid 

 coagulates by the action of heat or of alcohol, preserving, however, it* 

 transparency. According to recent analyses, the substance of the thyroid 

 body consists principally of albumen with traces of gelatine, stearine, oleine, 

 and extractive matter, besides alkaline and earthy salts and water. The 

 salts are chloride of sodium, a little alkaline sulphate, phosphates of potash, 



lime and magnesia, with 

 Fig. 646. some oxide of iron. 



A 



Fig. 646. TESICLES OP THE 

 THYROID GLAND ENLARGED 

 AND CONTAINING COLLOID 

 MATTER (from Kolliker). ^ 



One of the most fre- 

 quent pathological changes 

 to which the thyroid body 

 is subject consists in the 

 accumulation within its ve- 

 sicles of colloid substance : 

 this may occur without 

 giving rise to very great 

 enlargement of these vesi- 

 cles, but in certain forms 

 of goitre it distends them 

 to an enormous degree. 



Vessels. The arteries of the thyroid body (pp. 346 and 371) are the superior and 

 inferior thyroids of each side, to which is sometimes added a fifth vessel named the 

 lowest thyroid of Neubauer and Erdmann (p. 340). The arteries are remarkable for 

 their large relative size, and for their frequent and large anastomoses; they terminate 

 in a capillary network, upon the outside of the closed vesicles. The veins, which are 

 equally large, ultimately form plexuses on the surface, from which a superior, middle, 

 and inferior thyroid vein (pp. 453 and 460) are formed on each side. The superior 

 and middle thyroid veins open into the internal jugular; the inferior veins emanate 

 from a plexus formed in front of the trachea, and open on the right side into the 

 superior cava, and on the left into the brachio-cephalic vein. The lymphatics of the 

 thyroid body are extremely numerous and large, and are supposed to convey into the 

 blood the products formed within the organ. 



Nerves. The nerves are derived from the pneumogastric, and from the middle and 

 inferior cervical ganglia of the sympathetic. 



Development. Eemak states that the thyroid body is developed from the anterior 

 wall of the pharynx. In a human embryo at the third month, Kolliker found the 

 thyroid body consisting of isolated vesicles, with rounded cells in their interior. The 

 multiplication of these vesicles takes place, according to Kolliker, either by constric- 

 tion and subsequent division of one vesicle into two, or by a process of gemmation. 

 The transverse part of the gland is said to be developed subsequently to the two lateral 



