618 



AVES 



[CH. 



the quadrate is movable. It is to be remembered however that 

 the quadratojugal is here a small flexible bone, very unlike the- 

 great bony bar of Chelonia and Crocodilia. When a bony palate is 

 developed this is produced not by the union of outgrowths from the 

 palatine bones as in Crocodiles (and we may add as in Mammals), 

 but by outgrowths from the maxillary bones termed maxillo- 

 palatines which extend inwards towards the middle line dorsal to 

 the palatines. The hyoid apparatus consists of the second and 



third pairs of visceral 

 arches. The second 

 pair, which correspond 

 to the hyoid of Fishes, 

 are very short and con- 

 sist mainly of the me- 

 dian piece or .glosso- 

 hyal which is closely 

 connected to the me- 

 dian piece of the third 

 pair. The latter are 

 elongated rods to which 

 are attached the muscles 

 which protrude the 



FIG. 309. Third cervical vertebra of an Ostrich, tongue. As in the Rep- 

 Struthio camelus x 1. A, anterior, B, pos- tilia, the skull has One 



central knob or con- 

 dyle for articulation 

 with the backbone, not 

 two, as is the case with 

 the Amphibia and Mam- 

 malia. 



The features peculiar to the Bird are, firstly, the great elonga- 

 tion of the premaxilla carrying the beak this causes the nostrils to 

 be placed at the base of the snout instead of at the tip, as is the case 

 with most modern Reptiles, but a great many extinct Reptiles agreed 

 in this respect with Birds ; secondly, the enormous size of the orbit 

 and the absence of any bony bar to Separate it from the temporal 

 fossa, the hollow on the side of the skull, in which are situated the 

 muscles that close the jaws; and thirdly, the height and arched 

 character of the hinder part of the skull, which lodges the brain. 

 The bones of the skull are usually indistinguishably united in the 

 adult, are hollow and contain air, and are in consequence very light, 



-7 



terior, C, dorsal view. A and B after Mivart. 

 , Neural spine. 2. Neural canal. 3. Pre- 

 zygapophysis. 4. Postzygapophysis. 5. Pos- 

 terior articular surface of centrum. 6. Anterior 

 articular surface of centrum. 7. Canal 



between the capitulum and tuberculum of the 

 rudimentary rib. 8. Hypopophysis, a 



median ventral outgrowth of centrum. 



