M. Broca’s almost exhaustive remarks upon the anatomical, physiological, and pathological relations of this form of _tibia_ leave but little to be said under those heads. I would, however, venture to add a few words as to its ethnological significance. But before doing so I would remark that there appear to be two forms of platycnemism, apparently indicative of some difference in the cause or nature of this aberration from the more usual shape of the bone. To save many words, I subjoin outlines of several well-marked instances of platycnemic bones, all drawn of the natural size and in the same position, the letter (_a_) in each corresponding to the interosseous ridge, and (_b_) to the _crista_ or shin. The line _b c_, drawn through the _crista_ and the middle of the posterior surface of the bone, is bisected by another (_a d_), drawn at right angles to it, at the level of the interosseous ridge. In Fig. 47, which represents what may be regarded as a normal _tibia_, the length of that portion of the antero-posterior line which is behind the transverse line is to that of the anterior as 274 to 1,000, whilst in Fig. 48, taken from M. Broca’s outline of the Cro-magnon _tibia_, which would seem to represent the extremest degree of platycnemism as yet observed, the proportion in question is as 623 to 1,000. [Illustration: FIGS. 47, 48.] [Illustration: FIGS. 49, 50, 51.] Figs. 49, 50, 51, are taken from as many of the Gibraltar _tibiæ_,[110] in which the proportion varies from 600 to 523, whilst it will be observed that in Figs. 52, 53, 54, taken from the most platycnemic of the Perthi-Chwareu _tibiæ_, the proportion in one only differs in any considerable degree from the extreme normal proportion shown in Fig. 47; and in this it is as 512 to 1,000, whilst in Fig. 53, which is nevertheless undoubtedly platycnemic, the proportion is exactly the same as in the most triangular form of bone. It would seem, therefore, that platycnemism may arise from an unusual antero-posterior expansion of the bone, either in front or behind the level of the interosseous ridge. What this difference may indicate, or of what importance it may be in the consideration of questions relating to platycnemism, I am not prepared to discuss; but as in all probability it is connected with a difference in the cause of the deformation (if it be deformation), I have thought that the observation should be recorded, and would merely, in addition, remark that, so far as I have noticed, the occasional and not infrequent platycnemism observed in the shin-bones of negroes is what may be termed anterior. [Illustration: FIGS. 52, 53, 54.]