298 COMPARATIVE ZOOLOGY. 
another from the forehead to the most prominent part of 
the upper jaw, will include what is called the facéal an- 
gle, which roughly gives the relation between the two re- 
gions, and therefore the rank of the animal.’” In the 
cold-blooded Vertebrates the brains do not fill the erani- 
um; while in Birds and Mammals a cast of the cranial 
cavity well exhibits the general features of the cerebral 
surface. 
The subkingdom is divided into five great classes: 
Fishes, Amphibians, Reptiles, Birds,and Mammals. The 
first three are “cold-blooded,” the other two are “ warm- 
blooded.” Fishes and Amphibians have gills during the 
whole or a part of their lives, while the rest never have 
gills. Fishes and Amphibians in embryo have neither 
amnion nor allantois, while the other three are provided 
with both. 
Fishes and Amphibians agree in having gills, in want- 
ing amnion and allantois, and in possessing nucleated red 
blood-corpuscles. 
Birds and Reptiles agree in having no gills, but both 
amnion and allantois, in the articulation of the skull with 
the spine by a single condyle, in the development of the 
skin into feathers or scales, and in circulating oval, nucle- 
ated, red corpuscles. 
Mammals differ from Birds and Reptiles in having two 
occipital condyles, and their blood-corpuscles are not nu- 
cleated."” 
All Vertebrates are single and free. Mammals and a 
few Reptiles bring forth their young alive; the rest are 
oviparous. 
Crass 1.—Pisces. 
Fishes are the lowest of Vertebrates. “They fall far 
behind the rest in strength, intelligence, and sensibility. 
The eyes, though large, are almost immovable, bathed by 
