In such a mammal as a Beaver (Fig. 29), a line (a. b.) drawn through the bones, termed basioccipital, basisphe-

Fig. 29.—Longitudinal and vertical sections of the skulls of a Beaver (Castor Canadensis), a Lemur (L. Catta), and a Baboon (Cynocephalus Papio), a b, the basicranial axis; b c, the occipital plane; i T, the tentorial plane; a d, the olfactory plane; f e, the basifacial axis; c b a, occipital angle; T i a, tentorial angle; d a b, olfactory angle; e f b, cranio-facial angle; g h, extreme length of the cavity which lodges the cerebral hemispheres or 'cerebral length.' The length of the basicranial axis as to this length, or, in other words, the proportional length of the line g h to that of a b taken as 100, in the three skulls, is as follows:—Beaver 70 to 100; Lemur 119 to 100; Baboon 144 to 100. In an adult male Gorilla the cerebral length is as 170 to the basicranial axis taken as 100, in the Negro (fig. 30) as 236 to 100. In the Constantinople skull (fig. 30) as 266 to 100. The cranial difference between the highest Ape's skull and the lowest Man's is therefore very strikingly brought out by these measurements.

In the diagram of the Baboon's skull the dotted lines d²d² &c. give the angles of the Lemur's and Beaver's skull, as laid down upon the basicranial axis of the Baboon. The line a b has the same length in each diagram.