Charles K. Bardeen 273 



COCCYGEAL VERTEBRA. 



Since the valuable contributions of Fol, 85, who described 38 vertebrae 

 in the early human embryo, considerable attention has been devoted to 

 the development of the coccygeal vertebrae, especially from the point of 

 view of the number of vertebrse in embryos. The literature on the subject 

 has been summed up by Harrison, 01, and more recently by linger and 

 Brugsch, 03. Tlic later stages in the development of the coccyx have 

 been described by Steinbach, 89, who studied a large number of spinal 

 columns of foetuses, infants and adults. In a recent paper, 1904, I have 

 given a summary of the number of coccygeal vertebrae found in various 

 embryos and of the number of hremal processes found in the embryos 

 belonging to the collection of Prof. Mall. 



Without attempting here to enter into a detailed account of the condi- 

 tions found in these various embryos we shall pass at once to a consider- 

 ation of the more characteristic features of coccygeal development. The 

 differentiation of the coccj'geal sclerotomes begins at about the end of 

 the fourth week. Embryo II, length 7 mm., Pig, 1, Plate I. As a rule 

 at least six or seven membranous vertebrae are developed. The highest 

 relative differentiation of the coccygeal vertebrae occurs in the fifth and 

 sixth weeks. At this time dorsal processes connected by interdorsal 

 membranes extend as far as the 4th and 5th vertebra. Figs. 3 and 4, 

 Plate III, Fig. 41, Plate X. No distinct costal processes are, as a rule, 

 developed on any except the first coccygeal vertebra, but at the height of 

 development most of these vertebras have distinct haemal processes, first 

 described by Harrison, 01. These processes may also be seen on the more 

 distal sacral vertebrae. Fig. 41, Plate X. They usually disappear before 

 the embryo has reached a length of 20 mm., but the coccyx described by 

 Szawlowski, 02, suggests that occasionally they are retained until adult 

 life. 



Usually the bodies of the first five coccygeal vertebrae become chondro- 

 fied. The chondrofication of the more distal of these vertebrae is, as 

 pointed out by Rosenberg, 76, often very irregular. There may be sepa- 

 rate bilateral areas of cartilage or the two areas may be connected merely 

 anterior to the chorda dorsalis. The bodies of successive vertebrse may 

 be irregularly fused. 



As a rule the neural processes of the first coccygeal vertebra alone 

 become chondrofied and fused to the vertebral body. The others, as well 

 as the connecting interdorsal membranes, disappear. 



The cartilagenous coccygeal vertebrae are thus relatively less developed 

 than the membranous. It is probable that the osseous are less developed 

 than the cartilagenous. Tluis although Steinbach, 89, has made a strong 



