420 



ZOOLOGY 



SECT. 



is very striking. In the embryo (Fig. 1084) a vestige of the fifth 



digit (mt. tsl. 6) has been found 

 in the form of a small rod of 

 cartilage on the post-axial or 

 fibular side. One or two free 

 centralia may occur in the 

 mesotarsal joint. 



The skeleton is always more 

 or less pneumatic, but there is 

 no definite relation between 

 pneumaticity and power of 

 flight. A very usual arrange- 

 ment is for all the bones to 

 contain air except those of the 

 fore-arm and hand, shank and 



FIG. 1083. CtalluB bankiva (common Fowl). , ^ 



Innominate of a six days' embryo. Jl. ilium ; lOOt. >Ut in Apteryx, r en- 



Jg. ischium ; pb. pubis ; pp. pectineal process. arir i nrnp Snna hirrk 



(From Wiedersheim, after Johnson.) g mi lS, ana Ome bong-Dims 



the skull alone is pneumatic, 

 while in the Hornbill every bone in the body contains air. 



Myology. As might be inferred from a study of the skeleton, 

 the muscles of flight undergo a 

 great reduction, often amounting 

 to complete atrophy, in the Ratitae ; 

 and to a less degree in the flightless 

 Carinatae. The presence or ab- 

 sence of an ambiens and of cer- 

 tain other muscles in the leg and 

 in the wing furnish characters of 

 considerable classificatory import- 

 ance. 



Digestive Organs. In all 

 |l existing Neornithes the jaws are 

 covered by a horny beak and there 

 are no teeth. But that teeth 

 were present in the more primi- 

 tive Birds, and have gradually 

 been lost during the evolution 

 of the recent orders, seems cer- 

 tain from the fact that the cre- 

 taceous Birds were toothed. In 

 Hesperornis (Fig. 1064) there 



QT-O l/^-nrr nrminal taa+li in VinfTi FIG. 1084. Apteryx oweni. Left hind- 



are long conical teetn limb of embry0f dorsa i aspect, dist. 



jaws set in a continuous groove. SS& V^ wSiift 



In IchthyomiS (Fig. 1065) the Tib. tibia; tib. tibiale. (After T. J. 



teeth are thecodont, like those 



of the Crocodile, each being placed in a distinct socket. In 



Gastornis and in Odontopteryx, an extinct carinate form allied 



