xvi PREFACE!. 



chief constituent idea is ' work for a special end :' thus, the heart 

 is the ' organ ' of circulation ; the lungs, the ' organ ' of respira- 

 tion ; the liver, the ' organ' of bilification, &c. But also, incipient 

 stages in the development or formation of parts are called the 

 'organs' of such; e.g., the periosteum is the 'organ of bone,' 

 the pulp is the ' dentine organ ;' other parts of the growing 

 complex tooth are the ' enamel organ,' ' cement organ,' &c. The 

 parts in which independent cells, with special powers, originate, 

 are also called the 'organs' of such ; as, e.g., the ovary is the 

 ' organ of ovulation ;' the testis the ' organ of semination.' It 

 is obvious, however, that the part which the more or less con- 

 densed cellular basis, or ' stroma,' of the ovary or the testis may 

 take in the production of the germ-cells or sperm-cells and sperma- 

 tozoa is very different from that which the heart performs in the 

 motion of the blood, or the lungs in the mutation of the air 

 inspired. 



Zoological anatomy is now an indispensable instrument to the 

 classifier, if not to the determiner, of the species of animals. The 

 anatomist properly so called, but commonly qualified as the 

 ' comparative ' one, makes known the results and applications of 

 his comparisons of structure in zoological as well as homologi- 

 cal or anatomical works. The ' Regne Animal ' and the ' Lecons 

 d'Anatomie Comparee ' of Cuvier exemplify these different appli- 

 cations and ways of exposition of his science. 



As a zoologist or classifier, the anatomist avails himself of the 

 definite modification and full development of a part or organ, in- 

 dicating, and predicating of such conditions by special terms, 

 for the required characters. The ' fin,' the ' hoof,' the ' paw,' the 

 ' foot,' the ' hand,' are to him so many kinds of limbs, the presence 

 or absence of which serve to differentiate his groups ; anthropo- 

 tomical terms of parts of the brain reaching their full and cha- 

 racteristic development in Mammals or in Man, e.g., ' fornix/ 

 ' corpus callosum,' ' hippocampus minor,' ' posterior cerebral lobe,' 

 &c, serve and are used, absolutely, for the same end; so likewise 



