618 ZOOLOGY. 



Class VII. Ayes {Birds), 



General Characters of Birds. — We have met in the rep- 

 tiles, especially in the fossil forms, mam' characters indicat- 

 ing that birds ai-e by no means so specialized or so well 

 circumscribed a gi-oup as was formerly supposed. Such a 

 relationship between the two classes has recently been still 

 further exhibited by Meyer's discovery of Archceopteryx mac- 

 rura Owen of the Solenhofen slates of the Jurassic beds of 

 Germany, and by ^Marsh's discoyery of birds with teeth and 

 biconcave yertebrae in the Cretaceous rocks of Xorth Ameri- 

 ca. On account, therefore, of the close relations between 

 birds and reptiles, Huxley has placed these two classes in a 

 series called Sauropsida, which may be opposed to the Icli- 

 thyopsida (Fishes and Batrachians) on the one hand, and 

 the Mammalia on tlie other, by the following characters : — 



Sauropsida. — There are no mammary glands. There is 

 an amnion and an allantois ; the species are oyij)arous or 

 ovoyiyiparous, with reproductive organs and digestive canal 

 opening into a common cloaca, and "U'olfltian bodies replaced 

 functionally by permanent kidneys. There is no corpus 

 callosum, nor complete diaphragm. Eespiration is effected 

 by lungs, never by gills. The heart is three or four cham- 

 bered, and tliere are usually two or three aortic arches ; in 

 birds but one ; there are red oval nucleated blood corpuscles. 

 The bodies of the vertebrae are ossified, but without terminal 

 epiphyses. There is a single convex, occipital condyle, in 

 connection witli an ossified basi-occipital. The ramus of 

 the mandible consists of several pieces, the articulai' one of 

 which is connected with the skull by a quadrate bone. The 

 ankle-joint is between the proximal and distal divisions of 

 the tarsus. The skin usually developes scales or feathers. 



These important characters, derived from Huxley (as are 

 many of those given beyond for the class Aves), may remind 

 the student of the actual affinities between birds and rep- 

 tiles. The former are distinguished from other Sauroj'^ida 

 by the following peculiarities : — 



Ave^. — The body is coyered with feathers, a kind of der- 

 mal outgrowth found in no other animals. The fore limbs 



