Glass 5. Aves. 441 



for tie wliole length ; only in Arcliseopteryx were they separate. The 

 poUex has one or two joints^ the second digit two or three, the 

 third only one (rarely two) ; in Archseopteryx alone, the third 

 possessed three or perhaps four joints. In Birds which are capable 

 of flight, the arm when at rest lies along the body with the elbow 

 backwards; the forearm is directed anteriorly, and lies along the 

 arm, the ulna outwards, and the hand is curved at the wrist, so that 

 it lies along, and external to, the forearm, with the point backwards, 

 the inner edge (with the poUex) outwards. 



The pelvis closely resembles that of the Dinosaurians, but it is 

 further specialised (c/., p. 430). The ilium is elongate, and is 

 fused with a number of vertebrae (c/., p. 436) ; it is connected with 

 the other two bones at the acetabulum, which lies at its lower edge, 

 and in the formation of which, all three take part ; they are all fused 

 in the adult. The ischium, a strong bone directed backwards, 

 - runs almost parallel to the posterior portion of the ilium ; in most 



Pig. 369. Pelvis of a young American Ostrich (Rhea), il ilium, is isohiiim, 

 I acetabulum (with large perforation), p — p' pubis. — Orig. 



Birds, its hinder portion is firmly anchylosed in old age with the 

 ilium, whilst in Odontornithes and Struthious Birds it is either 

 quite free or only fused with the ilium posteriorly. The most 

 remarkable part of the avian pelvis is, however, the pubis. This 

 is a long thin bone stretching backwards parallel to the ischium, 

 with which it usually partially anchylosed. In some Birds (Odont- 

 ornithes, Eatitee, G-allinaceffi), there is a short process {p, Pig. 369) 

 at the upper end of the pelvis, just in front of the acetabulum; 

 but it is usually absent. It corresponds to the chief part of the 

 pubis of Dinosaurians, and to that bone itself in other Reptiles, whilst 

 the rest of the pubis [p') corresponds with the posterior pubic 

 process of Dinosaurians. Further, it must be noticed that 

 the pelvis of Birds is almost always quite open below, since neither 

 the ischium nor the pubis is fused with its fellow. In the hind 

 limb, the femur is relatively short; the fibula thin, imperfect, and 

 pointed at its lower end (except in Archgeopteryx) ; the tibia is long 

 and strong, and is furnished above, on the anterior surface, with a 



