284 



THE ANATOMY OF VEETEBRATED ANIMALS. 



bones ; and the intemasal septum, in front of the ethmoid, 

 may present very various degrees of ossification. Very 

 frequently, the interspace between the ethmoidal and the 

 intemasal ossifications is simply membranous in the adult, 

 and the beak is held to the skull only by the ascending 

 processes of the premaxillary bones, and by the nasal 

 bones, which are thin and flexible. By this means a sort 

 of elastic joint is established, conferring upon the beak a 

 certain range of vertical motion. In the Parrots, and some 

 other birds, this joint is converted into a true articulation. 



Fig. fi.3. 



J^rO 



Et/l 



DS 



so 



Fig. 83.— A longitudinal and vertical section of the posterior half of 

 the skull of an Ostrich. P., the pituitary fossa; asc.,psc., anterior 

 and posterior vertical semicircular canals of the ear. 



and the range of motion of the upper beak becomes very 

 extensive. 



The periotic capsule is completely ossified, and, as in 

 other Sauropsida, the epiotic and the opisthotic are anky- 

 losed with the occipital segment before they unite with the 

 pro-otic. In the primordial skuU of the bird the oKactory 

 organs are sun-oimded by cartilaginous capsules, the lateral 

 walls of which send in tvrbinal processes of very various 

 degrees of complexity. When the posterior wall of this 



