140 STRUCTURAL AND SYSTEMATIC ZOOLOGY 



and the face. The size of the cranial capacity, com- 

 pared with the area of the face, is generally the ratio 

 of intelligence. In the lower orders, the facial "part is 

 enormously predominant, 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. Compare 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 

 another from the forehead to the most prominent part 

 of the upper jaw, will include what is called \he, facial 

 angle, which roughly gives the relation between the two 

 regions, and the intellectual rank of the animal. 31 In 

 the cold-blooded vertebrates the brain does not fill the 

 cranium ; while in birds and mammals a cast of the 

 cranial cavity well exhibits the general features of 

 the cerebral surface. 32 



All higher vertebrates are single and free. Mammals 

 bring forth their young alive, the young before birth 

 deriving their nourishment directly from the mother 

 (viviparous). In almost all the others the nourishment 

 is stored up in the egg, which is laid before hatching 

 (oviparous), or is retained in the mother until hatched 

 (ovoviviparons\ as in some reptiles and fishes. 



Of the branch Chordata there are' three subbranches : 

 Adelochorda, Urochorda, and Vertebrata. The first in- 

 cludes Balanoglossus, a wormlike creature regarded by 

 some zoologists as being related to the backboned 

 animals, together with two other forms (Rhabdopleura 

 and Cephalodiscus) whose affinities are less plain. The 

 second includes the tunicates, while the great mass of the 

 Chordata belong in the third subdivision of the branch. 



