CLASSIFICATION OF BIRDS. 557 



CLASS VII. AVES. 



Feathered Vertebrates; jaws encased in horny beaks in existing forms : 

 the fore-limbs forming wings; warm-blooded; heart four-chambered ; 

 lungs with accessory air-sacs ; the bones dense, hollow ; oviparous ; egg* 

 very large, covered by a calcareous shell. 



Sub-class 1. Saurum. Tail as long as the body; head and fore limbs 

 reptilian; with feathers, scales, and teeth. (Archaeopteryx.) 



Sub-class 2. Odontornithes.* Vertebrae biconcave, or as usual ; jaws 

 slender, with teeth implanted in sockets or in grooves; mefra- 

 carpals co-ossified; sternum keeled or uukeeled ; wings well 

 developed (Ichthyoruis) or rudimentary (Hesperornis). 



Sub-class 3. liatitd 1 . Sternum smooth ; wings rudimentary. (Struthio). 



Sub-class 4. Carinatce. Sternum keeled ; wings well developed. (Tur- 

 clus. 



Laboratory Work. The student should prepare a skeleton of a hen or 

 any other bird, and compare it, and especially the skull and limbs, with 

 those of a reptile and a mammal. In dissecting a pigeon or fowl, at- 

 tention should be given to those points previously indicated in which 

 birds diverge from reptiles on the one hand and mammals on the other. 



CLASS IX. MAMMALIA (Mammal*). 



General Characters of Mammals. In the mammals, which 

 begin with the duck-bill, a creature in some respects re- 

 minding us of the birds, and end with man, we observe, 

 as compared with birds, an increased complexity of struc- 

 ture ; and in the nature of the work done by the different 

 organs, we may see a constant tendency to a development 

 of parts headward, so that the head becomes large in pro- 

 portion to the body, the brain increases in size, and the fore- 

 limbs finally become hands, ministering to the intellectual 

 wants of the animal. Also, as we ascend the series, the body, 

 from being horizontal, with limbs adapted for walking on all 

 fours, becomes finally in the apes semi-erect, in man wholly so. 

 The greatest step in advance over the reptiles and birds 



* It is doubtful if this is a natural group. Ichthyornis was probably 

 an archaic or generalized gull with teeth ; and the wingless Hesperornis 

 was the ancestor of the grebes and loons. (See also W. K. Parker.) 



