DEVELOPMENT OF EXTERNAL GENITALIA IN THE HUMAN EMBRYO. 77 



as in the embryo itself. The remains of the lateral buttresses arise just proximal 

 to this depression, spreading laterally for a short distance, then continuing basally 

 almost parallel to the axis of the phallus until they finally merge into the tissue at 

 its base. Unlike most of the younger embryos examined, there is almost no caudal 

 trend to these buttresses. The urogenital opening has deepened and become more 

 pronounced. It extends from the base of the phallus practically to its tip. In 

 this specimen it is not limited distally by an epithelial tag. The lack of this 

 appendage, useless as it at present seems, is probably due to some loss prior to or 

 during fixation. The distal portion of the groove (the glans portion) forms a 

 diamond-shaped dilatation extending to the proximal limits of the glans, the 

 remainder of the groove being constricted into a deep, narrow slit. The urethral 

 folds are rather pronounced elevations which diverge distally to merge into the 

 glans, while proximally they are considerably thickened into a pair of caudally 

 projecting, diverging masses (bulbo-urethral swellings?) which merge laterally 

 into the outlying labio-scrotal swellings. They are separated from the cavernous 

 portion of the phallus by broad concavities. Perhaps the most interesting feature 

 of this embryo is that it shows the apparent beginnings of the labio-scrotal swellings. 

 These are a pair of flat, elevated areas on either side of the base of the phallus with 

 which they seem to be continuous. The cranial margins of these areas are nearly 

 straight, extending at diverging angles into the inguinal regions, where their 

 cranio-lateral angles continue for a short distance as ridges of tissue. The caudal 

 margins appear as continuations of the diverging wings of the basal portions of the 

 urethral folds, forming sinuous curves to the caudo-lateral angles, from which 

 points they sweep cranially in rounding curves to the cranio-lateral angles, where 

 they unite with the cranial margins. This is the only specimen which shows these 

 swellings definitely connected with the base of the phallus. In all others in which 

 they are developed there is a groove (lateral phallic groove) on each side which 

 separates them from the base of the phallus. 



As regards the formation of the labio-scrotal swellings, my observations diverge 

 from the description given by Felix (1912, pp. 948-949) : 



"The cloacal tubercle is thus divided into the almost circular base of the phallus and 

 the scmilunar genital tubercle (fig. 639). This latter represents an originally impaired 

 structure lying cranial to the phallus and surrounding it on two sidfs; from it there are 

 formed later the two genital swellings. The genital tubercle is separated from the phallus 

 in female embryos by a deep groove which is the anlage of the later sulcus nympho-labialis, 

 the groove between the labia majora and minora. In the male embryos this groove is 

 absent from the beginning." 



My own findings indicate that the labio-scrotal swellings arise as paired out- 

 growths from the outlying tissue and not from a basal segment of the primary 

 tubercle. Furthermore, all but one of the specimens I have examined, both male 

 and female, show these swellings as separated from the phallus by the lateral phallic 

 grooves, a condition which is in striking contrast to the concluding statement made 

 by Felix. 



