Charles E. Bardeen 381 



and ischial processes of the pelvic blastema extend rapidly forward and 

 ventral to the obturator nerve they become joined by a condensation of 

 the tissue lying between them. Thus the obturator foramen of the 

 blastemal pelvis is completed. Figs. 5 and 6. Between the crest of the 

 ilium and the ventral extremity of the pubis dense tissue is formed to 

 give attachment to the oblique abdominal musculature. This represents 

 the embryonic Poupart's ligament and completes a femoral canal, Figs. 

 5 and 6. 



While the blastemal pelvis is being differentiated the formation of 

 cartilage in the ilium, ischium and pubis extends rapidly from the centers 

 indicated in Embryo CIX. In CXLIV, length IJ^ mm., Figs. 5, 6 

 and 54, the three cartilages are distinct. 



The iliac cartilage is a somewhat flattened rod with anterior and pos- 

 terior surfaces. Fig. 38. The anterior surface of the iliac cartilage at 

 first faces slightly laterally as well as anteriorly. Lubsen, 03, in an 

 interesting paper has shown the importance of this from the standpoint 

 of mammalian phylogeny. He considers a flat plate with median and 

 lateral surfaces to be the probable primitive form of ilium from which 

 the triangular form, on which Flower, 70, laid stress, is derived by a 

 lateral projection serving to divide the lateral surface into an anterior 

 iliac and a posterior gluteal portion. In man and some other mammals 

 the anterior iliac surface, according to Lubsen, comes to be turned 

 medially by a great extension of the lateral projection and a secondary 

 union of the abdominal musculature to this. In man, however, the 

 primitive iliac cartilage is a rounded plate of which the long axis of the 

 cross-section lies nearly at right angles to the median plane of the 

 embryo. On the whole it suggests the prism described by Flower. 



The pubic and ischial cartilages when first formed are mere rounded 

 masses of tissue lying in the center of their respective blastemal processes. 

 The acetabulum at this time is composed mainly of blastemal tissue but 

 the iliac and ischial cartilages form a part of its floor. Embryo CXLIV, 

 length 14- mm.. Figs. 5 and 6, Plate III. The pelvis of CR, length 

 13.6 mm., described by Petersen and pictured in Fig. 2, Plate I, of his 

 article, is of a stage of development similar to that of CXLIV. The 

 cartilages are slightly more advanced in development. The iliac carti- 

 lage is broader in an antero-posterior direction and extends to the 

 sacrum. He observed no dense tissue completing the obturator foramen 

 but this tissue is quite plain in the corresponding embryos of the Mall 

 collection, and it is described by Petersen for embryos Wi, length 

 15.5 mm., and Ob, length 15 mm., which are slightly more advanced 

 than CE. 



22 



