INTRODUCTION. 13 
Osteology, or the science of bones; and Odontography, or 
the natural history of teeth. 
Systematic Zoology is the classification of animals, or the 
study of animals, as to their kinds, giving to each a distinctive 
name and description. The systematic knowledge of the sev- 
eral classes, as Insects, Reptiles, and Birds, has given rise to 
subordinate sciences, like Hntomology, Herpetology, and Or- 
nithology.’* 
Distributive Zoology is the knowledge of the successive 
appearance of animals in the order of time (Paleontology in 
part), and of the geographical and physical distribution of 
animals, living or extinct, over the surface of the earth. 
Theoretical Zoology includes those provisional modes of 
grouping facts, and interpreting them, which still stand wait- 
ing at the gate of science. They may be true, but we can not 
say that they ae true. The evidence is incomplete. Such are 
the theories which attempt to explain the origin of life and 
the origin of species. 
Suppose we wish to understand all about the Horse. Our 
first object is to study its structure. The whole body is in- 
closed within a hide, a skin covered with hair; and if this 
hide be taken off, we find a great mass of flesh or muscle, the 
substance which, by its power of contraction, enables the ani- 
mal to move. On removing this, we have a series of bones, 
bound together with ligaments, and forming the skeleton. 
Pursuing our researches, we find within this frame-work two 
main cavities: one, beginning in the skull and running through 
the spine, containing the brain and spinal marrow; the other, 
commencing with the mouth, contains the gullet, stomach, 
intestines, and the rest of the apparatus for digestion, and 
also the heart and lungs. Examinations of this character 
would give us the Anatomy of the Horse, or, more precisely, 
LTippotomy. The study of the bones alone would be its 
Osteology ; the knowledge of the nerves would belong to 
Neurotomy. Tf we examined, under the microscope, the 
minute structure of the hair, skin, flesh, blood, and bone, we 
would learn its Histology. The consideration of the manifold 
changes undergone in developing from the ege to the full- 
* Numbers like this refer to the Notes at the end of the volume. 
