THE SKELETON 

 THE VERTEBRAL COLUMN 



THE vertebral column of an adult human being consists normally 

 of thirty-three to thirty-four vertebrae, numerical variation being 

 due to the inconstancy of those of the coccygeal or caudal series. 

 As might be expected from the study of other related organs (e.g. 

 the vertex coccygeus, the filiurn terminate, the arteria sacralis 

 media, certain muscles and nerves, and the coccygeal gland), 

 we here meet with evidence of degeneration and variation. This 

 is specially the case during development. It is, above all, the 

 caudal region which, in this respect, has claimed the greatest 

 attention of morphologists : and incidentally to the study of this 

 there arises the old controversy as to whether Man or his 

 ancestors possessed a tail. 



.At an early stage of development the human embryo 

 possesses at the posterior end of the body, clearly in direct 

 continuity with its developing axial skeleton, a free projecting 

 pointed appendage, bearing an undeniable resemblance to the tail 

 of a lower animal. This is delineated in Fig. 17, cd., and will 

 be further discussed as we proceed. At later stages of develop- 

 ment this organ is less conspicuous ; it gradually becomes shorter 

 and blunter, and is slowly, as it were, taken into the trunk. 

 For some time, however, a caudal prominence remains ; but 

 this at last either disappears altogether, or leaves, at the point 

 where its tip abutted against the integument, more or less 

 distinct traces known as the "vertex coccygeus" (cf. ante, 

 pp. 5 and 7). This is the normal course of development, but 

 occasionally a tail-like appendage is found in extra-uterine life. 

 An extensive literature exists on this subject, 1 and to it I 



1 Some of the alleged observations on this subject are not such as to awaken 

 confidence, and others refer to pathological cases or abortions, in which, among 

 other malformations, more or less developed caudal appendages occurred. Other 



