THE THYROID APPARATUS 33 



found during the first month of life, and they increase in number 

 with age, though they are not affected by the general nutritional 

 conditions. Petersen found glycogen in the parathyroid glands 

 of man at all ages ; its distribution was irregular, the principal 

 cells containing much, the oxyphile cells little. Glycogen is also 

 present in the connective tissue and the blood-vessels. Petersen's 

 view is endorsed by Guizetti, v. Verebely and Yanase. 

 H. Koenigstein considers that .upon histological grounds glycogen 

 may be regarded as a secretory product of the parathyroid glands. 



The parathyroid glands sometimes contain colloid, which 

 occurs in agglomerations situated, as a general rule, near the 

 edge, and which is occasionally contained in follicles similar to 

 those of the thyroid. There is a follicle-like arrangement of the 

 oxyphile cells, and at a later stage, the centre of this follicle 

 contains a colloid deposit, generally circular in shape, the edge 

 of which stains readily with eosin. Later on, the follicle cells 

 group themselves round the colloid to form a gland-tubule. 

 Colloid masses are also found within the larger cell-agglomera- 

 tions (Petersen). 



Chemical examination of the parathyroid glands is yet to 

 come. Gley proved the presence of iodine, though Chenu and 

 Morel found that both the external glands of the dog and the 

 rabbit contained something less than 0.025 mg., a proportion far 

 smaller than that in the same weight of thyroid tissue. 



According to Berkeley and Beebe, the parathyroid glands 

 contain a nucleo-proteid of specific activity. 



HISTORY OF THE DEVELOPMENT OF THE ORGANS 



OF THE NECK. 



To understand the anatomy of the parathyroid glands and 

 their relation to the thyroid, it is necessary to have some insight 

 into the history of the development of the organs of the neck. 

 This may be briefly stated as follows : 



At a very early stage of development, epithelial thickenings 

 form at the third and fourth branchial arches, one being situated 

 on the dorsal or cranial side, and one upon the ventral or sacral 

 side of the branchial clefts of both sides. The ventral thickening 

 of the third branchial cleft is the definitive primordial beginning 

 of the thymus gland, and is called thymus III. The thickening 

 upon the ventral side of the fourth branchial cleft was formerly 

 believed to be the primordial beginning of the thyroid gland, 

 but it is now very generally regarded as one of the beginnings of 

 the thymus, and is called thymus IV. 



It \vas formerly believed that the thyroid gland was derived 

 from the t\vo ventral portions of the fourth branchial cleft, in 

 combination with material derived from the median portion of the 

 fauces. This view has become very much modified, and it is now 



3 



