CLASSIFICATION OF TYPES. 363 



is absent, and the allantois rudimentary. There are no mam- 

 mary glands. 



2. The Sauropsida, including the Reptilia and A ves (fowl* and 

 pigeon). There is no gill-respiration, but gill-arches are present 

 in the embryo. There is almost always an epidermic exoskeleton 

 in the form of scales or feathers. The occipital region of the 

 skull is completely ossified, and there is one occipital condyle; 

 The mandible consists of several bones, and articulates with 

 the skull through the intervention of a quadrate bone. The 

 ankle-joint is between the proximal and distal divisions of the 

 tarsus. The temperature of the blood is near (reptilia) or con- 

 siderably above (aves) the normal temperature of the surrounding 

 medium. The red blood corpuscles are oval and nucleated. 

 The left systemic aortic arch is often (e.g. in all birds) suppressed. 

 The thoracic diaphragm is never complete or functional. The 

 Wolffian bodies are replaced by true kidneys. There is no 

 corpus callosum. The right oviduct and ovary may be (birds) 

 rudimentary. There is an amnion and a well-developed allan- 

 tois, the function of which is chiefly respiratory. There are no 

 mammary glands. 



3. The Mammalia , to which the rabbit belongs. There is no 

 gill-respiration, but gill-arches are present in the fcetus. The 

 epidermic exoskeleton consists of hairs. The occipital region of 

 the skull is completely ossified; and there are two occipital 

 condyles. The mandible consists of a single bone on each side, 

 and articulates directly with the squamosal of the skull. The 

 quadrate becomes an auditory ossicle. The ankle-joint is between 

 the tibia and the astragalus. The temperature of the blood is 

 more or less constant, and considerably above the normal tem- 

 perature of the surrounding medium. The red blood corpuscles 

 are generally round and not nucleated. The right systemic 

 aortic arch is suppressed. There is a complete and functional 

 diaphragm. The Wolffian bodies are replaced by permanent 

 kidneys. There is a corpus callosum in the brain. The foetus 

 has an amnion and allantois ; and in the higher forms a true 

 placenta is formed. Mammary glands supply the young with 

 nourishment. 



