Charles R. Bardeen ■ 283 



regular step in the jsrocess of attachment of ilinin to spinal column. 

 This I have previously pointed out (1904). Hagen, oo, has given an 

 account of the pelvis of an embryo of 17.5 mm., wliich corresponds with 

 the description given above. 



During the further development of the cartilagenous pelvis the ventral 

 extremities of its two halves, at first widely separated, in embryos of 

 20 mm. in close proximity, are finally united by a symphysis when the 

 embr3'o reaches a length of 25 mm. In an embryo of this length, 

 CCXXVI, the blastemal tissue of each half is fused in the median line 

 blit the cartilages are separated by % mm., although the width of the 

 pelvis at the rim is only 3 mm. In this embryo the obturator foramen 

 is completely enclosed by cartilage. In embryos of 30 mm. the pubic 

 cartilages are closely approximated in front. 



Petersen reconstructed the pelvis of an embryo of 29 mm., Lo^^, and 

 has given an extensive description of it. In essential features it corre- 

 sponds with the pelvis of Embryo CXLY, length 33 mm.. Figs. 11 and 

 12. The sacrum of this latter embryo is, however, composed of the 25th 

 10 29th vertebrse, while Petersen found the 30th vertebra of Lo^ belong- 

 ing to the sacrum. This variation is common in the adult. 



Of the characteristic features common to Lo^ and CXLV may be 

 mentioned the relatively great development of the sacral portion of the 

 ilium, with a large posterior-superior spine, the relatively slight develop- 

 ment of the abdominal portion, and the comparatively large part of the 

 pelvic entrance which is bounded by the sacrum. In the adult, according 

 to Engel, the sacrum bounds 26.2% of this. For the new-born female 

 the following figures are given by Fehling: sacrum, 28.9%; ilea, 29.2%; 

 pubes, 42.8% ; for the new-born male, 30.4%, 26.9% and 42.2%. For 

 Loj, the percentages are: 37.0%, 31.7% and 31.3%; for CXLV, 34%, 

 33% and 33%. 



In Loj the rim of the acetabulum is deepened by dense blastemal tissue. 

 In CXLV this has been in part converted into cartilage by extension 

 of processes from the ilium, ischium and pubis. The processes of the 

 ischium and pubis are fused with that of the ilium Init not with one 

 another, so that the cotyloid foramen is well marked. 



In both embryos the iliac blades bend more sliarply than in the new- 

 born and resemble in this respect tiie adult. The ischial spines are 

 relatively more developed and project more into the pelvis than do those 

 of the adult. 



The pelvis of Lo^ is that of a female ; the pelvis of CXLV that of a 

 male. It is of some interest to determine wliether or not sexual difi'er- 

 entiation is apparent. Fehling, 76, showed tliat during foetal life differ- 



