THE THYROID AND PARATHYROID BODIES 955 



of vesicles which are lined by a single row of cuboidal or columnar epi- 

 thelium, and contain a peculiar colloid materia 1 . The size and shape 

 of these vesicles differ greatly ; some of them attaining a diameter of 

 1.0 mm. Langendorff states that these acini are made up of two types 

 of cells, because while some of them appear to have reached adult size 

 and to be actively secreting, others seem to be held in reserve until 

 called upon to take the places of those torn away and discharged in the 

 secretion. 



The thyroid is a very vascular organ, receiving 560 c.c. of blood 

 per 100 grams of substance in the course of a minute. 1 Its five supply 

 channels are the right and left superior and inferior thyroid arteries, 

 branches of the external carotid, and the thyroidea ima, which ascends 

 upon the trachea and is a branch of the subclavian arteries. Each 

 lobe is drained by three collecting channels, namely the superior, 

 middle and inferior thyroid veins. This gland is also equipped with 

 an intricate system of lymphatics which, however, do not communi- 

 cate directly with the colloid vesicles. Its nerve supply is derived 

 from the superior and inferior laryngeal nerves. 



Position and Structure of the Parathyroid Glands. The parathy- 

 roids 2 usually present themselves 'as four small rounded masses em- 

 bedded in the substance of the thyroid. They are oval in shape, 

 measuring about 6 mm. in length and 3 to 4 mm. in breadth, and their 

 combined weight rarely exceeds 0.10 gram. 3 One pair of them is 

 usually found near the level of the lower border of the cricoid carti- 

 lage, between the wall of the esophagus and the lateral mass of the 

 thyroid, while the second is situated as a rule opposite the third or 

 fourth ring of the trachea in or near the lower pole of each lobe. 4 

 Accessory parathyroids are encountered at times along the trachea 

 and even in the cavity of the thorax. 



The cells composing these bodies are epithelial in character and 

 are arranged in palisade-like columns which are connected with one 

 another by unusually vascular connective tissue. In many cases 

 this tissue is so well developed that the entire gland appears to be sub- 

 divided into many smaller lobules. Its parenchyma is made up, 

 on the one hand, of large polygonal chief cells, the cytoplasm of which 

 does not stain well, and, on the other, of cells possessing a delicate, 

 granulated interior which stains intensely with eosin and other acid 

 dyes. The parathyroids may also contain follicles which are filled 

 with a colloidal material similar to that occupying the vesicles of the 

 thyroid. 



Extirpation of the Thyroid and Parathyroids. It was formerly 

 believed that the thyroid regulates the blood-supply of the brain 



1 Tschuewsky, Pfliiger's Archiv, xcvii, 1903, 210. 



2 Discovered by Sandstrom, Upsala Lakarefor. Forh., xv, 1880, and described 

 by Kohn, Archiv fur mikr. Anat., xlv, 1895. 



3 Thomson, The Thyroids and parathyroids throughout vertebrates, Phil, 

 transact., Roy. Soc., 1911. 



4 Fischer, Archiv fur Anat., 1911. 



