12 NATURAL HISTORY OF BIRDS. 



only three; tlie latter are (iriiily anchjloscJ with the luuibo-sacral vertebiu>, except in 

 the peii{;;uiiis. Caudal vertebraj occur in numbers from seven to fifteen (21 V), the largest 

 number beiiit; found in the sulvdass Saurunv, enibracintj the Jurassic Arch(iopten/.r. 

 Next in number i:omv!i J/enjurorii is, from the cretaceous formation, with twelve, while 

 most of the living birds have from seven to ten. In Arc/iwojJteri/x they were all free, 

 each su])porting a pair of tail feathers ; in Ilesperornis the last ones were anchylosed, and 

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

 which are still se])arate in the embryo, become fused completely together in the adults, 

 so as to form a single bone, which, from its peculiar sha])e, has been called the 

 ' jiloughshare bone,' or the pygostyle ; it 8ui)ports 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 vertebrae, including those fonning the 

 pygostyle. 



The breast-bone is generally iprii\ ided with a keel, wliicli, 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, //I's- 

 jwroriiis, JS'otoniis, the doilo, Cnemioruiit, and the large ground-parrot or kakajjo 

 (Striijops) from New Zealand. It must be remembered that a sternal (ejiisternal) keel 

 is not an entirely unknown thiTig anumg the rejitiles. Sternal ribs are connecteil with 

 the foremost dorsal ribs liy hinge joints ; the ribs are provided with uncinate ]>rocesses ; 

 these are wanting in the fossil Arc/uvoj>tcri/.r and in C/uiuna among living birds, but 

 are, on the other hand, found in some reptiles, for examj)le, in JIaUeria and in the 

 crocodiles. 



The shoulder girdle consists of a long, narrow, and curved sca]>ula, a form which 

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

 bone is quite flattened ami l>r<)adcned behind in the penguins. The collar-bones 

 usually unite into a 'wish-bone,' or ' mei'rylhought ' (J'lircu/tiin). They are sej)- 

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

 the ostriili, llic kiwis, a few parrots, etc. The arm-bones offer but little fur i-cniark. 

 We Jnay i-efcr to the arrangement of the elbow-joint, which is so constructed as to 

 allow movement in one plane for extension and tlexion oidy, but not for supination 

 and ])ronation ; the same remark applies to the carpal joint ; both joints are stiti' and 

 nearly immov.able in the penguins. Birds h.ave, 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 oidy a single 

 carpal. It is interesting to note that this w.as also the condition in Archct'optcn/.); The 

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

 first finger, or ])ollex, generally ln'ing indicated by a ])roi'i'ss at the |>roximal end of the 

 second metatarsal. Archa'opteryx differs remarkably by having all three metacarpals 

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

 an accessory bone supi>orting a thick, horny s])ur, as in the screamer, the s])urwinged 

 goose, and others, wliich should not be confoim<led with the claws at the end of the 

 fingers, a mistake not at all uncommon. 



Corresponiling to the three metacarjtals, the number of the fingers is also three, a 

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

 iHiniber of )ihalanges in the three fingers left, — the radial one usually having one, the 

 7niildle finger three or two, and the ulnar finger sometimes three, but oftener two or 



