188 Henry Fox 



While jDrimaril}' concerned with the development of the pharynx in 

 man, Hammar also examined a series of rabbit embryos, and while he 

 does not in his article treat of them particularly, he yet mentions that 

 he finds an essential agreement in the formation of homologous parts 

 in both forms. Accordingly, he is inclined to assume that the essential 

 features of the development in man will hold good in the case of other 

 mammals. 



Hammar's first article was followed by a second on the fate of the 

 second pharyngeal pouch. This is the last article of his I have seen, 

 and, so far as I know, he has not published any articles on the fate of 

 the last two pouches. 



The appearance of Hammar's paper seemed to me at first to do away 

 with the necessity of further study of the first two pairs of pouches, 

 but as Gaupp had already expressed the idea — ^based upon the conflict- 

 ing statements of earlier investigators — that the formation of these 

 parts probably differed considerably in different species of mammals, I 

 concluded that a further contribution on the subject in the three species 

 examined by me would not be without value. Moreover, as Kastschenkd, 

 the chief authority on the process in the pig, had declared that the 

 middle ear tube did not arise in any way from the first pharyngeal 

 pouch, I considered this an additional reason for continuing my 

 investigation. 



The results of this investigation, so far as the first and second 

 pharyngeal pouches are concerned, are largely confirmatory of the con- 

 clusions reached by Hammar in man and the rabbit. The probability 

 therefore is that the development of these parts is essentially similar 

 in the majority of placental mammalia. 



In the case of the third and fourth pharyngeal pouches I have 

 obtained results which clear up certain details about which there has 

 been much conflict of opinion. Among these may be mentioned the 

 determination of the origin and structure of the carotid gland, a recon- 

 ciliation of the conflicting statements regarding this structure made by 

 Kastschenko and Prenant, a confirmation of the ectodermal origin of 

 the so-called thymus superficialis of Kastschenko, and finally the origin 

 of a second structure — beyond doubt the glandule thyroidienne of Pre- 

 nant — from the fourth pouch. 



My earlier studies were made by the aid of the wax reconstruction 

 method. Later, owing to the lack of facilities for continuing the use 

 of this method, I adopted the method of graphic projection, making 

 dorsal, ventral and lateral views of each stage studied. 



