AVES BIRDS. (j()9 



and the nasal cavity indicates, by its extent, that it is now 

 well adapted to investigate the odorous properties of the air 

 taken in for respiration. The septum narium completely divides 

 the nose into two lateral chambers of considerable extent, which 

 individually communicate with the pharynx (fig- 277, c) ; and, 

 upon the outer wall of each compartment, three convoluted 

 laminae, covered with a most delicate Schneiderian membrane, re- 

 present the turbinated bones of Mammalia, and increase the olfactory 

 surface. Of these, the middle turbinated bone (jig* 277, a) is the 

 largest ; but the superior appears to be the most important, as it is 

 upon this that the olfactory nerve is principally distributed, inso- 

 much that Scarpa considered that the comparative powers of smell 

 possessed by different birds might be estimated by the develope- 

 ment of this portion of the olfactory organ. The olfactory nerves 

 (Jig. 277, i), as in Reptiles, still enter the nose without dividing, 

 so that there is no cribriform plate to the ethmoid bone. The 

 nostrils are simple apertures, perforating some part of the horny 

 beak covering the upper mandible, and are never provided with 

 moveable cartilages or muscles, as those of Mammalia will be found 

 to be. 



(679.) The eye of a Bird is an optical instrument of such ad- 

 mirable construction, that, did not the nature of this work compel 

 us to adopt the strictest brevity in our descriptions, it might well 

 tempt us to indulge in lengthened details relative to the adaptation 

 and uses of its various parts. If we contrast the Bird with the 

 Reptile, or more especially with the Fish, and consider the totally 

 different circumstances under which these animals exercise the sense 

 of vision, we might well expect extraordinary modifications in the 

 structure of their organs of sight. The Fish, immersed in a dense 

 medium, can see but to a very limited distance around it ; and the 

 sphericity of the crystalline lens, with the consequent contracted 

 antero-posterior diameter of the eye-ball, at once testifies how small 

 is the sphere of vision commanded by the finny tribes. The Bird, 

 on the contrary, dwelling in the thin air, and not unfrequently soar- 

 ing into regions where that air is still further rarified, must sur- 

 vey an horizon even more extensive than that enjoyed by the 

 terrestrial Mammal ; while, from the rapid movements of the 

 feathered races, it becomes absolutely requisite that the focus of the 

 eye shall continually vary between the extremes of long and short 

 sighted vision. The birds of prey, as they fan the air at an altitude 

 which places them almost beyond the reach of human sight, or sail 



