5 88 THE POPULAR SCIENCE MONTHLY. 



touching the most prominent parts of the forehead and upper jaw, the 

 intersected angle is called the facial angle" (vol. ii., p. 5*72, "Anatomy 

 of Vertebrates "). 



The relation of the face is not to the base of the skull, or the plane 

 from the floor of the nostrils to its articulation to the backbone, but to 

 the axis of the body ; for the face, in the lowest class of animals that 

 have a backbone, the fish, is in line with the base of the skull, the 

 axis of the body, and the dorsal surface of the animal ; and in man, 

 the highest class, the face is in line with the abdominal surface, and 

 axis of the body. But the base of the skull does not keep in harmony, 

 but varies irregularly. Then, there are numerous other elements than 

 the bones at the base of the skull, that are factors in the aspect of the 

 face, as, the modified development of other bones of the skull, peculiar 

 development of bones of the face, and relation of the bones of the face 

 that are not attached to the sJcull, but to other facial bones. 



To make the subject more clearly comprehensible, it will be neces- 

 sary to trace more in detail the development of the division of ani- 

 mals to be considered. 



The subject of the facial angle has occupied the attention of phi- 

 losophers from the earliest antiquity. Their theories, though vague, 

 unsatisfactory, and uninteresting in themselves, yet tend conclusively 

 to show that some patent general principle underlies the whole domain 

 of the subject. Confined, as they were, to the narrow limits of the 

 varieties of the human race, they would get only a part of the evi- 

 dence that is so beautifully illustrated, when we include the whole 

 sub-kingdom of animals to which we belong. 



At the beginning of the present century, Cuvier, Yon Baer, and 

 others, discovered and established the great laws of evolution. The 

 laws thus elucidated were : 1. That the entire animal kingdom origi- 

 nates from an ancestral egg ; eggs, too, though differing in physical 

 appearance, that are quite similar in structure. 2. That every animal, 

 in its evolution, had to pass through the several stages of ovulation, 

 fertilization, germination, and development, before it could maintain 

 an independent existence. 3. That in their development they assumed 

 but few primary structural patterns or types. 



After the promulgation of the above doctrines, a series of investi- 

 gations ensued, which brought naturalists to approximate a general 

 agreement that there are only five general morphological or form- 

 types of animals. Every animal, then, of the entire animal kingdom, 

 must be classed in one or the other of these five sub-kingdoms, and 

 each division thus classed has one fundamental plan of structure. The 

 only way in which the animals of each sub-kingdom can differ is in 

 the manner of executing their physiological functions. 



In considering, then, any of the great physiological and philosophi- 

 cal questions that are based upon a uniformity of primitive type-devel- 

 opment, we find that many useful lessons may be learned by including 



