. Anthropology . , is the alveolo-condy-lean plane, determined by three readily accessible points, viz. thealveolar, or middle point of the superior alveolar arch, and the mostsloping points of the inferior surface of the occipital condyles. Itis represented in Eig. 5 by the line A P Q, and in Fig. 7 by theline C C. It is in relation to this alveolo-condylean plane, whichis also called the natural plane of the base of the skull, that measures the degree of inclination or of straight direction ofvision, or, rather, of the plane passing through the two orbital axes. * We refer to the mem
. Anthropology . , is the alveolo-condy-lean plane, determined by three readily accessible points, viz. thealveolar, or middle point of the superior alveolar arch, and the mostsloping points of the inferior surface of the occipital condyles. Itis represented in Eig. 5 by the line A P Q, and in Fig. 7 by theline C C. It is in relation to this alveolo-condylean plane, whichis also called the natural plane of the base of the skull, that measures the degree of inclination or of straight direction ofvision, or, rather, of the plane passing through the two orbital axes. * We refer to the memoir of M. Broca, Sur les Angles Occipitaux, Eevue dAnthropologic, vol. ii. p. 193, for the second decimals. More-over, we purpose in this volume confining ourselves generally to the first. 56 PHYSICAL dHABACTEBS. [Chap, l. The dihedral angle which they form by being prolonged i&called positive, or ordinary, when the plane of vision is raised, andthe meeting of the two takes place backward; and negative,, when. Fig. 7.—A, Horizontal axis of the orbit passing through the-centre of the-optic foramenbehind and through the centre of the base of the orbit in. front; 0 0,. Alveolo-condylean plane, or plane of Broca (see APG-5 Fig. 5), The other references arethe same as in that figure. it is depressed, and the meeting is in front. In the following tablethe former has no sign before it; the latter is accompanied by thesign - . The second column refers to another character which willcome afterwards. In Fig. 7, the alveolo-condylean plane, C C, is-parallel, as we see, to the plane of vision, A. 43 gorillas1 orang 4 pithecians 5 cebians 1 maki3 clogs 3 rabbits 2 horses 1 wild boar Orbito-alveolo- Biorbital condylean angle. angle. - 08 47° 47 19° 31 39° 04 28° 53 45° 90 15° 44 52° 24 7° 22 41° 59 23° 58 73° 72: 24° 94 70° 51 31° 15 143° 43 36° 09 109° 19 47° 61 98° 94 Chap, i.] PHYSICAL CHARACTERS. 57 Thus we find that the vision of Man is sensibly horizontal i
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