AVES. 221' 



both sexes resemble the former. When the adult male and 

 female are of the same colour, the young ones have a livery 

 peculiar to them. 



The brain of Birds has the same general characters as that 

 of other Oviparous Vertebrata, but is distinguished by its very 

 great proportionate size, which often surpasses even that of 

 this organ in the Mammalia. This volume principally depends 

 upon tubercles, analogous to the corpora striata, and not upon 

 the hemispheres, which are narrow and without circumvolu- 

 tions. The cerebellum is tolerably large, and almost without 

 lateral lobes, being chiefly constituted by the vermiform pro- 

 cess. 



The rings of the trachea are entire ; there is a glottis at its 

 bifurcation most commonly furnished with peculiar muscles, 

 which is called the inferior larynx ; this is the spot where 

 the voice of birds is produced ; the immense volume of air 

 contained in the air sacs contributes to its strength, and the 

 trachea, by its various forms and motions, to its modifications. 

 The superior larynx, which is extremely simple, has but little 

 to do with it. 



The face, or upper mandible of Birds, consisting chiefly of 

 their intermaxillaries, is lengthened out behind into two arches, 

 the internal of which is composed of the pterygoid and palatine 

 bones, and the external of the maxillaries and jugals, both of 

 which rest on a movable tympanic bone, commonly called the 

 square bone, analogous to that of the drum of the ear ; above, 

 this same face is articulated with the cranium, or united to it 

 by elastic laminae, a kind of union which always allows the parts 

 some degree of motion. 



The horny substance which invests the two mandibles, per- 

 forms the office of teeth, and is sometimes so jagged as to re- 

 semble them ; its form, as well as that of the mandibles which 

 support it, varies extremely, and according to the kind of food 

 used by each species. 



The digestion of Birds is in proportion to the activity of their 

 life, and the force of their respiration. The stomach is com- 

 posed of three parts : the crop* which is an enlargement of 



