VERTEBRATA. 297 
or both. Vertebrates are the only animals which breathe 
through the mouth. 
The nervous system has two marked divisions: the cer- 
ebro-spinal, presiding over the functions of animal life 
(sensation and locomotion); and the sympathetic, which 
controls the organic functions (digestion, respiration, and 
circulation). In no case does the gullet pass through the 
nervous system, as in Invertebrates, and the mouth opens 
on the side opposite to the brain. Probably none of the 
five senses are ever altogether absent. The form of the 
brain is modified by the relative development of the vari- 
ous lobes. In the lower Vertebrates, the cerebral hemi- 
spheres are small—=in certain Fishes they are actually 
smaller than the optic lobes—in the higher, they nearly 
or quite overlap both olfactories and cerebellum. The 
brain may be smooth, as in most of the cold-blooded an- 
imals, or richly convoluted, as in Man. 
The skull is distinctly set apart from the spinal column, 
except in Fishes. It is bony in Mammals, mingled bone 
and cartilage in Birds and Reptiles, and in Amphibians 
and Fishes mainly or wholly cartilaginous. The human 
skull contains fewer bones than the skull of most animals, 
excepting Birds. The skull of all Vertebrates is divisi- 
ble into two regions: the cranium, or brain-case, and the 
face. The size of the cranial capacity, compared with the 
area of the face, is generally the ratio of intelligence. In 
the lower orders, the facial part is enormously predomi- 
nant, the eye-orbits are directed outward, and the occipital 
condyles are nearly on a line with the axis of the body. 
In the higher orders, the face becomes subordinate to the 
cranium, the sensual to the mental, the eyes look forward, 
and the condyles approach the base of the cranium. Com- 
pare the “snouty” skull of the Crocodile and the almost 
vertical profile of civilized Man. A straight line drawn 
from the middle of the ear to the base of the nose, and 
