372 B. F. KINGSBURY 



ment of the original anlage, it is difficult to determine. A care- 

 ful study of their histogenesis in suitable material is much needed. 

 It seems to be quite unnecessary to introduce figures in illustra- 

 tion of their position and general development in addition to 

 those already published (cf. Grosser '11 and Hammar '11). 

 It may be permitted, however, to call attention to the evident 

 mistake in lettering in the otherwise typical figure pubhshed by 

 Grosser ('10) and subsequently reproduced in the Keibel and 

 Mall Handbook (vol. 2, fig. 330.) On the left, epithehal body III 

 should obviously be epithehal body IV, and vice versa; the 

 position is in itself characteristic. At this place I also desire to 

 mention an error in the description of figures 1 and 2 in my 

 earlier article ('14 b) : Th. = thyreoid, thy. = thymus. 



In facing the problem of the morphological significance of 

 the parathyreoid bodies, the investigator^ — as in the case of 

 the thymus — encounters the two alternative interpretations of 

 intrinsic branchiomeric organs whose anlage is located in definite 

 regions of the branchial pouch, and the interpretation that their 

 development is a factor of their relative position and relations, 

 and hence extrinsic, to a marked degree. The former is the 

 generally accepted view, and their development from an epithe- 

 hal area of definite location, seems to confirm its soundness. 

 I am inclined to beheve, however, that further investigation 

 will support the alternative. In the early development of both 

 parathyreoids III and IV, in embryos of (7.5 mm.) 8.3 mm. to 

 10 mm. the epithehum undergoing the 'parathyreoid tras- 

 formation' is that immediately adjoining the corresponding 

 aortic arches III and IV, respectively. These arches here pass 

 close to and in intimate contact with the branchial epithelium 

 upon the anterior and dorso-lateral aspects of the respective 

 pouches. It is here that the parathyreoids are being differ- 

 entiated, and the mesenchyme between the two structures, vas- 

 cular endothehum and branchial epithelium (parathyreoid anlage) 

 is scanty or lacking (figs. 26, 29, 30). If this correlation pos- 

 sess morphological significance, it will be found in other mam- 

 mals, and whether or not this is the case has not been ascertained. 

 The existence of such an association is man in presented, there- 



