XIII 



PHYLUM CHORDATA 



433 



S'v'llll?f 



FIG. 1072. Callus bankiva (common Fowl). 

 Innominate of a six days' embryo. Jl. ilium ; 

 Js. ischium ; pb. pubis ; pp. pectineal process. 

 (From Wiedersheim's Comparative Anatomy, 

 after Johnson.) 



The bones of the hind-limb are very uniform throughout the 



class, but the form of the 



tarso-meta tarsus of Penguins 

 is worthy of notice. It is 

 short and wide, its three con- 

 stituent metatarsals, though 

 fused, are clearly distinguish- 

 able throughout their whole 

 length, and the resemblance 

 to the homologous part in 

 Iguanodon is very striking. 

 In the embryo (Fig. 1073) a 

 vestige of the fifth digit (Mt. 

 tsl. 5) has been found in the 

 form of a small rod of cartilage 

 on the postaxial or fibular 

 side. One or two free cen- 

 tralia may occur in the meso- 

 tarsal joint. 



The skeleton is always more or less pneumatic, but there is no 

 definite relation between pneumaticity and power of flight. A very 



usual arrangement is for all the 

 bones to contain air except those 

 of the fore-arm and hand, shank 

 and foot. But in Apteryx, Pen- 

 guins, and some Song-birds the 

 skull alone is pneumatic, while in 

 the Hornbill every bone in the 

 body contains air. 



Myology. As might be in- 

 ferred from a study of the skele- 

 ton, the muscles of flight undergo 

 a great reduction, often amount- 

 ing to complete atrophy, in the 

 Ratitas ; and to a less degree in 

 the flightless Carinatae. The pre- 



Mttsl.i ^TW\ ^|W" \ sence or absence of an ambiens 



Mtf 7 -r*Jf P vl \ an< ^ ^ certa ^ n otner muscles in 



* 2 ( ? i % ] ^ e ^ e anc ^ * n ^ e w ^ n & f urn i sn 



\ ^ / characters of considerable classi- 



\^ I / ficatory importance. 



Digestive Organs. In all 

 FIG. io73.-A P teryx oweni. Left hind- existing Neornithes the iaws are 



limb of embrvo. dorsal asrject. dtst. *? - . . * . , 



covered by a horny beak and 

 there are no teeth. But that 

 teeth were present in the more 

 primitive Birds, and have gradually been lost during the evolution 



1073. Apteryx oweni. Left hind- 

 limb of embryo, dorsal aspect, dist. 

 distal e ; Fe. femur ; Fib. fibula ; Jib. fibu- 

 lare ; Mt. tsl. 15, metatarsals ; Tib. tibia ; 

 tib. tibiale. (After T. J. Parker.) 



