. Anthropology. ical, 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 poiats of the inferior surface of the occipital condyles. Itis represented in Fig. 5 by the line A P Q, and ia Fig. 7 by theline C C. It is in relation to this alveolo-condylean plane, whichis also called the natiiral plane of the base of the skuU, that measures the degree of incliaation or of straight direction ofvision, or, rather, of th« plane passiag through the two orbital axes. * We refer to the
. Anthropology. ical, 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 poiats of the inferior surface of the occipital condyles. Itis represented in Fig. 5 by the line A P Q, and ia Fig. 7 by theline C C. It is in relation to this alveolo-condylean plane, whichis also called the natiiral plane of the base of the skuU, that measures the degree of incliaation or of straight direction ofvision, or, rather, of th« plane passiag through the two orbital axes. * We refer to the memoir of M. Broca, Sur les Angles Occipitaux, Eevne dAnthropologie, vol. ii. p. 193, for the second decimals. More-over, we purpose in this volnme confining ourselves generally to the first. 56 PHYSICAL CHABACTEES. [Chap. i. The dihedral angle which they form by being prolonged iscalled positive, or ordinary, when the plane of vision is raised, andthe meeting of the two takes place backward; and negative, when. FiQ. 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 Brooa (see A P G, Fig. 6). 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 wiUcome afterwards. In Fig. 7, the alveolo-condylean plane, C C, isparallel, as we see, to the plane of vision, A. Orbito-alveolo- Biorbital cundylean angle. angle. 43 - 08 47° 47 5 gorillas 19° 31 39° 04 1 orang 28-53 45° 90 4pitheoians 15° 441 52° 24 5 oebians 7°22 41° 59 1 maki 23° 58 73° 72 3 dogs 24° 94 70° 51 .S rabbits 31° 15 143° 43 2 horses 36° 09 109° 19 1 wild boar ... 47° 61 98° 94 ?Chap, i.] PHYSICAIi CHAEACTEES. 57 Thus we find that the vision of Man is sensibly horizon
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