OSTEOLOGY 133 



from them. The prepubic or pectineal process is large in 

 the struthious birds, in the tinamous, and in a few carinates, 

 such as Geococcyx, It has received much attention as the 

 possible equivalent of the reptihan pubis, the bird's so-called 

 pubis being in that case the homologue of the posterior pubic 

 process of the reptile. The dinosaurians seemed at one time 

 to have been the means of solving the questions involved ; 

 for in some of them there is a backwardly directed pubis, 

 not quite so bent as in the bird, from the anterior and upper 

 end of which a stout bone, considered to be the homologue 

 of the pectineal process, is directed forwards. This latter, 

 however, is clearly a part of the pubis, while the pectineal 

 process is at least not always a product of the pubis, being 

 sometimes purely iliac in origin, sometimes partly pubic and 

 partly iliac. It may be that the missing prepubic process of 

 the dinosaurian pelvis is represented by the remarkable 

 bones ankylosed to the ostrich's pelvis anteriorly, and con- 

 tinued forwards by- a cartilaginous tract, which were dis- 

 covered by Darwin and Gareod. This will reduce the 

 pectineal process to the level of a mere projection of the 

 pelvis of no particular significance save as a secure hold for 

 the important ambiens muscle which is there attached. In 

 any case it is safe to assert that wherever that process is pre- 

 sent and long the ambiens is also present and well developed. 



Among carinate birds the pelvis does not show a great 

 variability of form. The pelvis is either broader or narrower, 

 being excessively narrow in the Colymbi. The proportions 

 of the preacetabular and the postacetabular regions also 

 differ, as do their relative breadths. 



It is noteworthy that the pubis is sometimes defective in 

 the middle, appearing then to consist of a proximal and 

 distal portion unconnected in the dry skeleton. The fact 

 also that but few muscles arise from the pubis seems to show 

 that it is in a condition of degeneration. 



In Archceopteryx alone are the elements of the pelvis 

 not ankylosed together. 

 ; The acetabulum of all birds except DromcBus is perfo- 



