INTRODUCTION. 



11 



FIG. 4. Under view of the 

 skull of the capercallie 

 (schizognathous). The 

 letters as before. 



Fig. 5, we also find the maxillo-palatines (mxp) separate medially and from the vomer 

 (yo), but the latter is truncate in front and cleft behind, embracing the basisphenoid 

 rostrum (R) between its forks. Finally, the saurognathous pal- 

 ate, which is peculiar to the super-family Picoideae, is particu- 

 larly remarkable for having the two lateral halves of the vomer 

 separate. 



It may be well, however, to state that these characters are 

 by no means always very trenchant, as two types often inter- 

 grade insensibly, while in other cases we find them sharply ex- 

 pressed in nearly related forms, as an example of which we 

 shall only mention the closely allied genera Megalaima and Tet- 

 ragonops, besides several of the birds of prey. 



The anterior nostrils are situated at the base of the beak 

 (except in some Struthious birds, for example, Apteryx, in 

 which they open near its tip), and may have a well-defined and 

 rounded hinder edge, a condition called holorhinal by Pro- 

 fessor Gai'rod, or be prolonged backwards as a fissure, when the 

 term schizorhinal is used. A peculiar feature of the bird's 

 beak is the flexibility of its union to the frontals by the long 

 nasals and frontal processes of the premaxillae ; this is carried 

 to an extreme in the parrots, in which the connection between 

 the beak and the forehead is formed by a movable joint. The 



two halves of the lower jaw anchylose early, except in some fossil forms, and the sym- 

 physis (and consequently the gonys) is of very varying length. None of the recent 

 birds have teeth in their jaws, and this negative character was a long time regarded as 



distinctive of the class, as compared with the great ma- 

 jority of reptiles and mammals. Rudimentary teeth 

 have lately been demonstrated in the grooves of the 

 lower jaw of the embryonic penguin. It is also claimed 

 that rudiments of teeth, in sockets and covered by den- 

 tine, have been found in embryos of parrots. Late in- 

 vestigations have failed to discover the dentine. Besides, 

 important groups of fossil birds have of late been dis- 

 covered, which were more or less richly supplied with 

 teeth ; as, for instance, Arc/ice opteryx, Laopteryx, Gas- 

 tornis, Argillornis, Hesperornis, Ichthyornis / the last 

 had teeth in sockets, while those of Hesperornis were 

 fixed in grooves, and were shed in a similar way to those 

 of the reptiles. 



The " saddle-shaped " vertebra is peculiar to the bird 

 FIO. 5. under view of a sparrow-like class, that is to say, the vast majority of living birds have 

 Sribft gB * tll00-)l Thelet " the antesacral vertebra? saddle-shaped, a form not seen 



elsewhere ; but opisthocoelian vertebra? may occasionally 



occur, being even the rule among the penguins, \vhile biconcave or amphiccelian verte- 

 brae, such as we find in fishes and many batrachians and reptiles, particularly fossil forms, 

 are one of the most remarkable features of the extinct Archceopteryx, Ichthyornis, Apa- 

 tornis, and, probably, Laopteryx. The number of cervical vertebra? varies between nine 

 and twenty-five, those of the dorsal region between four and eleven, or, exceptionally, 



pmx 



mxp 



