BIRDS. 205 



this is the case, the young of both sexes resemble the female. 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 character as that of other 

 Oviparous Vertebrata, but it is distinguished by its very great propor- 

 tionate size, which often surpasses even that of this organ in the Mamma- 

 lia. This volume principally arises from tubercles, which are analogous 

 to the corpora striata, and not upon the hemispheres, which are narrow 

 and without convolutions. The cerebellum is tolerably large, and almost 

 without lateral lobes, being chiefly constituted by the vermiform process. 



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

 bifurcation most commonly furnished with peculiar muscles, which is called 

 the inferior larynx ; this is the point where the voice of birds is pro- 

 duced ; the immense volume of air contained in the air sacs contribute to 

 its strength, and the trachea, by its various forms and motions, to its mo- 

 difications. The superior larynx, which is extremely simple, enters the 

 inferior, but has little to do with the voice. 



The face, or upper mandible of Birds, consisting chiefly of their inter- 

 maxillaries, 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 hone, analogous to that of the drum of 

 ear ; above, this same mandible is articulated with the cranium, or united 

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

 some degree of niotion. 



The horny substance which invests the two mandibles, performs the 

 office of teeth, and is -sometimes so jagged as to resemble 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 composed of three parts : 

 the crop, which is an enlargement of the oesophagus ; a membranous sto- 

 mach, in the thickness of whose parietes are a multitude of glands whose 

 juices moisten the food; and finally, the gizzard, armed with two power- 

 ful muscles, and united by two radiated tendons, which are lined inter- 

 nally with a cartilaginous kind of velvet. The food is the more easily 

 ground there, as birds constantly swallow small stones, in order to increase 

 their triturative power. 



In the greater part of the species which feed exclusively on flesh or 

 fish, the muscles and villous coat of the gizzard are greatly attenuated; 

 and it seems to make but a single sac with the membranous stomach. 



The dilatation of the crop is also sometimes wanting. 



