234 



AVES. 



'/if 



of the lower jaw and the maxillo-palatine apparatus are enabled by 

 special articular arrangements to move on the temporal bone and 

 on corresponding processes of the basisphenoid. The quadrate, which 

 is articulated to the temporal bone, has, besides the articular surface 

 of the lower jaw, movable connections with the long rod -like 

 quadra to- jugal, and with the usually styliform pterygoid which runs 

 obliquely inwards, while the base of the upper beak presents a thin 

 elastic place below the frontal bone, or is separated from the frontal 

 bone by a transverse movable suture. When the beak is opened, 

 and the lower jaw is moved downwards, the pressure on the quadrate 

 bone is transferred to the rod-like quadrato-jugal and the pterygoid 



bones, and from these is transmitted 

 partly directly and partly by means of 

 the palatine bones to the upper beak, so 

 that the latter must be more or less 

 raised at that point. Therefore, when 

 the mouth is opened, the end of the 

 beak is raised. The greater part of the 

 upper beak is formed by the unpaired 

 prsemaxilla, with the sides of which the 

 maxillae are fused, while an upper median 

 process ascends between the nares and 

 unites with the frontal on the inside of 

 the nasal bones. 



The hyoid bone (fig. 649) is prolonged 

 into a posterior rod ; its anterior * cornua 

 are usually two-jointed and are not con- 

 nected with the skull, but in some cases 

 they are much elongated and arch over 

 the skull as far as the forehead (Woodpecker). They then consti- 

 tute in connection with the muscles of their sheath a mechanism for 

 the protrusion of the tongue. 



In the vertebral column (fig. 650), a very long movable cervical 

 region, a rigid dorsal and pelvic region and a rudimentary, only 

 slightly movable caudal region can be distinguished. In Birds 

 there is no separation of thoracic and lumbar regions as in Mammals, 

 since all the dorsal vertebrae bear ribs and the region corresponding 

 with the lumbar region takes a share in the formation of the sacrum. 

 The cervical and dorsal regions also are not sharply distinct from 



Fig. 649. Hyoid apparatus of 

 Corvus comix. Co, body of 

 hyoid ; Zh, cornua ; Ent, ento- 

 glossal bone. 



* Usually described as the posterior cornua. Ed. 



