SKELETON. 



433 



attached to a process — ^the clavicular process — of the dorsal end 

 of the coracoid. A foramen, called the foramen triosseum, is 

 thus left between the three bones of the shoulder girdle at the 

 point where they meet one another. The two clavicles are 

 ankylosed together ventrally and may at this point be attached 

 by ligament or even ankylosed to the keel of the sternum. The 

 clavicles are small and remain distinct from one another ventrally 

 in some birds (parrots, owls, toucan, emeu) and are rarely absent 

 (some Ratitae, some parrots). 



The humerus has an expanded head, a preaxial and postaxial 

 tuberosity, of which the postaxial is the larger, and a deltoid 

 ridge which extends for a short distance down the shaft of 

 the bone from the preaxial tuberosity. The pneumatic foramen 

 is on the proper dorsal face of the proximal end of the bone 

 close to the postaxial tuberosity. The ulna is stouter than 

 the radius and often presents a number of tubercles caused 

 by the attachment of the wing quills. The carpus con- 

 sists of two bones only, but in the young bird it is said that a 

 distal carpal row of three pieces which later fuse \^dth the meta- 

 carpus can be made out. Three digits are present, viz. digits 

 1, 2, and 3. The metacarpals of these are all fused together ; 

 that of the pollex is much shorter than the others and carries two 

 phalanges. The metacarpals of the other two digits are united 

 at each end ; digit No. 2 has two or three phalanges and digit 

 No. 3 has one phalanx (two in the ostrich). The terminal pha- 

 lanx of the pollex is often unguiculate, as is in rare cases (ostrich) 

 that of the second digit. In the emeu and apteryx the fu-st and 

 third digits are absent in the adult, and in some birds the wing 

 bones are considerably reduced {Hesperornis) and ahnost or 

 quite absent (Moas). In Archceopteryx the metacarpals are 

 separate and all the digits bear claws. In some embryo birds 

 a rudiment of digit No. 4 is said to have been detected. 



In the pelvic girdle the ilia are remarkably expanded antero- 

 posteriorly both in front of and behmd the acetabulum, and at- 

 tached by their whole length to the compound sacrum. The 

 ischia are directed backwards parallel to the hmder part of the 

 iUum to which they are attached posteriorly converting the ilio- 

 ischiatic notch into a foramen. The pubes are slender bones 

 directed backwards parallel to the ischia, with which they often 

 unite posteriorly. The pubes and ischia do not unite with each 



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