AVES. 527 



loped, nearly withuut lateral lobes, and consisting almost entirely of the 

 vermiform process. _ 



The trachea is formed of entire rings. At its bifurcation is a glottis 

 furnished with a set of muscles called the lower larynx. This organ pro 

 duces the voice of birds, which has great compass owing to the large volum 

 of air contained in the air vessels. The voice is modified by the length an 

 width of the trachea. The upper larynx is very simple. 



The anterior extremities, or wings of birds, are formed for sustaining 

 them in flight, but are neither adapted for prehension nor standing. The 

 body has a forward inclination, and tlie toes are considerably produced, to 

 assist in sustaining them in an upright posture. The pelvis is much elonga- 

 ted, in order to furnish attachment to the muscles which support the trunk 

 upon the thighs. There is also a beautiful provision in nature, by which 

 birds are enabled to sleep with certainty perched on trees. A set of muscles 

 trtke their rise in the pel vis and extend themselves to the toes, so that the 

 weight of the bird alone is sufficient to close them. 



The lower extremities are composed of a femur, a tibia, and a peroneum 

 which is articulated to the femur by a spring, whose extension is maintain- 

 ed without the muscles being exerted. The tarsus and metatarsus consist 

 of a single bone only. 



Most birds undergo two moults annually ; and in some species the winter 

 plumage ditfers considerably from that of the summer ; and the male and 

 female also vary in colour, in many species. 



The digestive function in bird's is very rapid. The stomach is composed 

 of three parts ; namely, the crop, the succenturial ventricle, and the gizzard. 



CLASSIFICATION OF BIRDS. 



The orders and genera into which birds are divided, are established chiefly 

 from the formation of the bill and feet. The classification adopted is that 

 of Temminck, who posseses a deeper knowledge of this subject than any other 

 naturalist. It is remarkable for its simplicity. He divides this class into 

 sixteen orders, namely,^ 



I. Rapaces. — Birds of prey. 



II. Omnivores. — Those which live on all kinds of food. 



III. Insectivores. — Birds which feed on insects- 



IV. Granivores. — Birds which feed on grain. 



V Ztgodactyli — Birds which have two toes before and one behind. 



VI. Anisodactyli. — Birds which have the exterior toe joined to the raid, 

 die one at the base. 



VII. Alcyones.— Birds with three toes before, united, and one behiud ; 

 the tarsi being very short. 



VIII. Chelidones.— Birds with short legs, three toes before, divided, or 

 only united at the base by a short membrane ; the back toe often reversible. 



IX. CoLUMBjj.— Birds with three toes before, entirely divided, and one 

 behiud. 



X. Gai,linj3.— Birds with three toes before, united by a membrane ; the 

 back toe joined to the tarsus above the joint of the other toes. 



XI. Alectorides.— Birds with the tarsus long and slender; three toes 

 bi'fiire and one behind ; the articulation of tlie posterior one higher thiiu 

 tliose before. 



