U COMPARATIVE ANATOMY. 



nection with Birds. At the present day it cannot appear doubtful 

 to any morphologist that the latter are descended from Reptilian 

 ancestors. 



Birds. In Archaeopteryx, found in the Solenhofen slates of 

 the Bavarian Jurassic, and already mentioned on p. 22, many of the 

 special peculiarities of Reptiles and Birds are united. The hinder 

 extremities are distinctly Reptilian, as is also the tail, which, like 

 that of a Lizard, is composed of numerous elongated free vertebra?. 

 A covering of true feathers, on the other hand, characterises it as 

 a Bird : the biserial arrangement of the tail-feathers is seen in 

 Fig. 33. 



Fie. 33. TAII, OF AreliKOptcryx. 



The vertebral column of Birds corresponds with that of Reptiles 

 not only in its phylogenetic relations, but also ontogenetically. In 

 both groups the notochord eventually disappears entirely, and the 

 "whole skeleton becomes strongly ossified. 1 The pelvis of Bird- 

 embrvos, like that of existing adult Reptiles, is attached to the 

 vertebral column by 1w<> vertebra' only ; during further develop- 

 ment, however, a number of oilier vertebra; (thoracic, lumbar, and 

 caudal) become fused with the sacrum (Fig. 34). 



A further difference between the vertebral column of Reptiles 

 and I'.irds is seen in the character of the caudal region in the latter 

 grfiup, which always remains apparently rudimentary. In this 

 peculiarity existing Birds stand in sharp contrast to their Jurassic 

 ancestors (sec above). 



It must, however, be well understood that the J>ygo style of 

 Birds may be made up of six or more fused caudal vertebra', and in 



1 ] ch t li yrn is (from the Ann rirun Cretaceous), as well as Archeeopteryx, pos- 

 sessed biconciivr vertebrae. Tin- samr tyi' of vnirhni is to be nirt \\iih in many 

 : ',.,/. in tin- Kn:i]i'iv:mii;i), ami in MOIIC existing ll<-|itilrs I A^' alalmta ;unl 

 Satti i i;ij, ay well as in iimni nf tli IV. . i .nulal \ . il. ITJ in < xistin.ir I'.irds. 



