STUDIES OF THE DEVELOPMENT OF THE HUMAN" 

 SKELETON. 



(a). The Development of the Lumbar, Sacral and Coccygeal Vertebra. 



(b). The Curves and the Proportionate Regional Lengths of the Spinal 

 Column during the First Three Months of Embryonic Development. 



(c). The Development of the Skeleton of the Posterior Limb. 



BY 

 CHARLES R. BARDEEN. 



Professor of Anatoviy, The University of Wisconsin. 

 With 13 Plates. 



The following studies on skeletal development are based upon embryos 

 belonging to the collection of Prof. Mall, at the Johns Hopkins Uni- 

 versity, Baltimore. I am greatly indebted to Prof. Mall for their use. 



A. 



THE DEVELOPMENT OF THE LUMBAR, SACRAL AND COCCYGEAL 



VERTEBRA. 



Eecently I have given an account of the development of the thoracic 

 vertebrge in man (This Journal, Vol. IV, No. 'I, pp. 163-175). In the 

 present paper it is my purpose to describe the special features which 

 characterize the differentiation of the more distal vertebrae. 



During the early stages of vertebral development the skeletal apparatus 

 of the various spinal segments is strikingly similar. This is shown in 

 Fig. 1, Plate I, which illustrates the spinal column of Embryo II, 

 length 7 mm. Yet even during the blastemal stage some regional differ- 

 entiation becomes visible. The costal processes of the thoracic vertebrae, 

 for instance, develop much more freely than those of other regions. It 

 is, however, during the chondrogenous period that the chief regional 

 features appear. 



To what extent morphological similarity in the sclerotomes and sclero- 

 meres indicates equal formative potentiality experiment alone can deter- 



Ameeican Journal of Anatomy. — Vol. IV, 

 21 



