438 



Vertebrata. 



j ugal, external to that already noticed; it is a thin rod of bone, 

 and is formed posteriorly by the quadratojugal, medianly by 

 the jugal, and anteriorly by a process of the maxilla; in the 

 adult these bones are often anchylosed. The beak is attached 

 above to the rest of the skull, by the upper portion of the- pre- 



Pig. 362. 



Fig. 363. 



rig. 362. Skull of a Eaven from the rentral 

 side, g foramen magnum, j jugal, ma: maxilla, 

 ns nasal septum, pa palatine, pt pterygoid, q 

 quadrate, v vomer. — Orig. 



Fig. 363. Diagrammatic figures to iUuetrate 

 the movement of the beak in Birds, n nasal 

 septum, h posterior membranous portion of this, 

 orbit, I quadrate, h jugal, v pterygoid, g palatine. 

 In A the bill is raised, in JB lowered. — Orig. 



maxilla, and by the nasal, which lies behind the nares ; the posterior 

 portions of these bones (premaxillse and nasals) are, however, 

 flattened, thin, and elastic,* and since the lower part of the nasal 

 septum is membranous, Birds are able to move the beak up 

 and down. The movement upwards is effected by the forward 

 motion of the lower end of the quadrate, by which the two bony 

 bridges are pushed forwards, and pressed against the lower, hinder 

 portion of the beak, so as to send its point upwards ; the movement 

 downwards, on the other hand, is the result of the retraction of the 

 quadrate. As for other characters, it may be noticed, that most of 

 the sutures have disappeared, even in the young animal, owing to 

 the fusion of the bones ; further the cranial-cavity is very large as 

 compared with that of most Reptiles. 



* In the Parrots and some others which have a specially movable beak, this bony 

 mass is interrupted by a narrow strip of connective tissue. 



