PUBO-FEMOKAL REGION. 135 



man than in any other animal (Figs. 107-4 and £). In him, the 

 most internal part of the passage is left unfilled, and this unfilled 

 space forms the femoral or crural canal through which femoral 

 hernia may escape. The crural passage is relatively larger in 

 women than in men, owing to the greater size of the female 

 pelvis, and hence femoral hernia are much more common in 

 women than in men. Some hint as to the method of treatment 

 of hernia in man may be obtained from a consideration of the 

 arrangement of structures which prevent them in other animals. 



THE PELVIC FLOOR. 



The Coccyx. — It is necessary to consider the coccyx here 

 because the changes which it has undergone in the evolution of 

 the human body are intimately connected with the formation of 

 the pelvic floor. 



The coccyx in man is commonly composed of four vertebrae, 

 more or less vestigial in nature, which represent the basal caudal 

 vertebrae of tailed mammals. Evidence of their vestigial or 

 retrograde nature is to be found in : 



(1) Only their centra are developed — with the exception of the 

 first, which shows partial formation of transverse processes and 

 neural arches (superior cornua) ; 



(2) Delay in the appearance of the centres of ossification. 

 These, instead of beginning in the 7th week as in a typical 

 vertebra, commence after birth. The centre for the 1st coccygeal 

 vertebra appears in the 1st year, that for the 4th vertebra about 

 the 25th year; the 2nd and 3rd at intermediate periods. 



(3) Late in life, between the 40th and 60th year, the verte- 

 brae fuse together, and then unite with the sacrum. 



The number of coccygeal vertebrae varies ; four is the normal 

 number, but there may be three or five. In the young foetus 

 (2nd month) there are commonly 5, 6 or 7 (Eosenberg). The 

 first coccygeal vertebra may join the sacrum, making 6 sacral 

 vertebrae. 



The evidence of the former existence of a true tail in the 

 ancestral human stock consists of: 



