1272 



SPLANCHNOLOGY 



ure on an average about 6 mm. in length, and from 3 to 4 mm. in breadth, and 

 usually present the appearance of flattened oval disks. They are divided, accord- 

 ing to their situation, into superior and inferior. The superior, usually two in number, 

 are the more constant in position, and are situated, one on either side, at the level 

 of the lower border of the cricoid cartilage, behind the junction of the pharynx 

 and esophagus. The inferior, also usually two in number, may be applied to the 

 lower edge of the lateral lobes, or placed at some little distance below the thyroid 

 gland, or found in relation to one of the inferior thyroid veins. 1 





Common carotid 

 artery 



Right parathy- 

 roids 



Inferior thyroid 

 artery 



Remnant of laryn- 

 geal nerve 



FIG. 1177. Parathyroid glands. (Halsted and Evans.) 



In man, they number four as a rule; fewer than four w^ere found in less than 1 

 per cent, of over a thousand persons (Pepere 2 ), but more than four in over 33 per 

 cent, of 122 bodies examined by Civalleri. In addition, numerous minute islands 

 of parathyroid tissue may be found scattered in the connective tissue and fat of 

 the neck around the parathyroid glands proper, and quite distinct from them. 



Development. The parathyroid bodies are developed as outgrowths from the 

 third and fourth branchial pouches (Fig. 1175). 



A pair of diverticula arise from the fifth branchial pouch and form what are 

 termed the ultimo-branchial bodies (Fig. 1175): these fuse with the thyroid gland, 

 but probably contribute no true thyroid tissue. 



1 Consult an article "Concerning the Parathyroid Glands," by D. A. Welsh, Journal of Anatomy and Physiology, 

 vol. xxxii. 



2 Consult Le Ghiandole paratiroidee, by A. Pepere, Turin, 1906. 



