498 



among whom may be mentioned more especially Holl (1882) and 

 Paterson (1893), have attacked Rosenberg's hypothesis, it has re- 

 ceived a fairly general, if sometimes qualified acceptance. It was 

 adopted by v. Koelltker (1879), and more recently Petersen (1893) 

 has partially endorsed it. In 1899 Rosenberg defended his hypothesis 

 against the attacks which had been made upon it. 



In connection with a study of the development of the human ske- 

 leton which I have been making I have had occasion to determine 

 the relation of the thorax and pelvis to the spinal column in the em- 

 bryos belonging to the collection of Professor Mall, at the Johns 

 Hopkins University, Baltimore^). I have compared the conditions 

 there found with those reported for embryos of corresponding stages 

 by other investigators, and with the numerical variations in the verte- 

 brae described by those who have studied the subject in infants and 

 adults. 



For the sake of convenience in the present study four periods 

 may be recognized in the development of the spinal column and its 

 appendages: 1) the prepelvic period; 2) the period of chondrofication ; 

 3) the period of ossification, subdivided into prenatal and postnatal; 

 and 4) the adult period. 



I. Prepelvic Period. 

 By this is meant the stage preceding the union of the iliac bla- 

 stema with the costal processes of the sacral vertebrae. It extends 

 up to about the end of the fifth week. In a previous article (1901) 

 a description was given of the relations of the limb-buds to the body 

 segments in the embryos belonging to the collection of Professor Mall 

 and to that of Professor His. Pictures are there given of the relation 

 of the femoro-pelvic blastema to the spinal segments in Embryo CLXIII, 

 length 9 mm, age about 4V2 weeks, and Embryo CIX, length 11 mm, 

 age about 5 weeks. In Embryo CLXIII the iliac portion of the ske- 

 letal blastema, or sclero-blastema, of the limb lies opposite the costal 

 processes of the 22d, 23d and (24th) vertebrae [3d, 4th and (5th) 

 lumbar]. In Embryo CIX the sclero-blastema of the ilium lies oppo- 

 site the 22d, 23d, 24th and (25th) vertebrae [3d, 4th and 5th 

 lumbar and (1st sacral)]. Corresponding stages are pictured by 

 Petersen for the His embryos: S, length 12.6 mm, and Cr, length 

 13.6 mm, age about 5 weeks. In Embryo S the iliac blastema lies 



1) I am greatly indebted to Professor Mall for the use of this 

 collection. 



