12 NATURAL HISTORY OF BIRDS. 



only three ; the latter are firmly anchylosed with the lumbo-sacral vertebrae, except in 

 the penguins. Caudal vertebrae occur in numbers from seven to fifteen (21 ?), the largest 

 number being found in the sub-class Saimirae, embracing the Jurassic Archceopteryx. 

 Next in number conies Hesperornis, from the cretaceous formation, with twelve, while 

 most of the living birds have from seven to ten. In Archceopteryx they were all free, 

 each supporting a pair of tail feathers ; in Hesperornis the last ones were anchylosed, and 

 there is reason to believe that it had no rectrices at all ; in other birds, the last ones, 

 which are still separate in the embryo, become fused completely together in the adults, 

 so as to form a single bone, which, from its peculiar shape, has been called the 

 'ploughshare bone,' or the pygostyle ; it supports the oil-glands, and, indirectly, the 

 rectrices, which, on account of the shortening of the tail, have been forced out to the 

 extreme end of the vertebral column. It has been suggested that the number of 



^^ 



rectrices correspond with the number of caudal vertebra, including those forming the 

 pygostyle. 



The breast-bone is generally provided with a keel, which, however, becomes greatly 

 reduced or is wanting altogether in those forms in which the fore limbs have ceased to 

 act as locomotive organs (wings or paddles), as, for instance the ostriches, kiwis, Iles- 

 perornis, IVbtornis, the dodo, Cnemiornis, and the large ground-parrot or kakapo 

 (/Strigops) from Xew Zealand. It must be remembered that a sternal (episternal) keel 

 is not an entirely unknown thing among the reptiles. Sternal ribs are connected with 

 the foremost dorsal ribs by hinge joints ; the ribs are provided with uncinate processes ; 

 these are wanting in the fossil Archceopteryx and in Chauna among living birds, but 

 are, on the other hand, found in some reptiles, for example, in Ilatteria and in the 

 crocodiles. 



The shoulder girdle consists of a long, narrow, and curved scapula, a form which 

 among the reptiles is found in the pterodactyls ; while, on the other hand, the shoulder 

 bone is quite flattened and broadened behind in the penguins. The collar-bones 

 usually unite into a 'wish-bone,' or 'merrythought' (furculum). They are sep- 

 arate in a few forms, as in the emu and some owls, while they are altogether absent in 

 the ostrich, the kiwis, a few parrots, etc. The arm-bones offer but little for remark. 

 \Ve may refer to the arrangement of the elbow-joint, which is so constructed as to 

 allow movement in one plane for extension and flexion only, but not for supination 

 and pronation ; the same remark applies to the carpal joint; both joints are stiff and 

 nearly immovable in the penguins. Birds have, when adults, usually two carpal 

 bones, one ulnar and one radial (as have also the crocodiles), but a few deprived 

 of the power of flight --for instance, the cassowary and the kiwi have only a single 

 carpal. It is interesting to note that this was also the condition in Arclueopteryx. The 

 metacarpals are usually three in number and more or less fused together, that of the 

 first finger, or pollex, generally being indicated by a process at the proximal end of the 

 second metatarsal. Archceopteryx differs remarkably by having all three metacarpals 

 free and well developed. The carpus is sometimes provided on the anterior side with 

 an accessory bone supporting a thick, horny spur, as in the screamer, the spurwinged 

 goose, and others, which should not be confounded with the claws at the end of the 

 fingers, a mistake not at all uncommon. 



Corresponding to the three metacarpals, the number of the fingers is also three, a 

 free pollex being absent in the penguins and cassowaries, however. Judging from the 

 number of phalanges in the three fingers left, the radial one usually having one, the 

 middle finger three or two, and the ulnar finger sometimes three, but oftener two or 



