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STKUCTUEE AND CLASSIFICATION OF BIRDS 



direction ; the ischium and the pubis look downwards and 

 slightly backwards ; at the end of the pubis, near to where 

 it comes into contact with the iliac portion of the cartilage, 

 is a forwardly directed process, the prepubic process. This 

 primitive state of affairs has been most nearly preserved in 

 Apteryx and Dinornis ; in these birds the pubis and ischium 

 are free from each other distally and from the ilium ; their 

 direction is, however, more backwards than in the embryo, 

 and the prepubic process is relatively smaller. In all other 

 birds the pubis and the ischium lie in a line more parallel 



Pig. 75 — Pelvis of Dinoenis (aftee Mivaet). J- Natueal Size. 

 il, ilium ; p^ pubis ; pSy iuterobturator process ; Ip, pectineal process. 



with the ilium, and there is a greater or less connection 

 between the several bones. This is seen in a less developed 

 condition in the struthious birds and tinamous than in any 

 others. In the tinamous, in fact, the pubis and ischium are 

 quite free from each other distally, and from the ilium. In 

 the ostrich the pubes unite in a ventral symphysis ; in Bhea 

 there is a remarkable modification induced by the meeting 

 of the ischia. The details of the struthious pelvis will be 

 found described under the description of that group. In 

 carinate birds the ischium is for the greater part of its extent 

 fused with the ilium, a foramen only — the ischiadic foramen 

 — being left anteriorly. The pubes join to a less extent with 

 the ischia, and are sometimes (e.g. Colymbus) quite free 



