3d. The eminences of reflection are those under which a tendon passes, in deviating from its primitive course; such is the hook of the pterygoid apophysis, the malleolar extremity of the fibula, &c. Almost all these eminences have a slope or excavation in one direction, connected in the opposite with a ligament, so as to form a ring for the passage of the tendon. 4th. The eminences of impression are those which arise, when the different organs form on the osseous surfaces excavations that separate these eminences, which in fact only appear because the bone at this place remains at its ordinary level. The cerebral and muscular impressions are given as examples of this arrangement. But are these impressions really the effect of the compression of the organs on the bone, or do they arise from the laws of the osseous development, laws which give to the bones forms accommodated to the surrounding organs? I adopt more readily the second than the first of these opinions, which has been thought very probable from the effect of aneurisms upon bones that are contiguous to them, which are worn and gradually destroyed by them. But let us remark that if the muscles, the brain, and the vessels by their pressure, had upon the bones in a natural state, an action analogous to that of aneurism, the state of the parts ought to be the same as in that case. The compact layer ought to be destroyed where these depressions are, and leave in its place an unequal, ragged surface, but the contrary happens, which makes me think, that what is commonly called the impression of organs, is only a natural effect of ossification. V. _Of the Osseous Cavities._ The osseous cavities are very numerous; those only which are found on the exterior of the bones will be treated of. They are divided, like the eminences, into articular and non-articular. The first will be examined, with the analogous eminences, in the chapter on articulations. Among the second there are cavities, 1st, of insertion; 2d, of reception; 3d, of slipping; 4th, of impression; 5th, of transmission; 6th, of nutrition. 1st. The cavities of insertion give attachment to the aponeuroses of the muscles, to the ligaments, &c. They have the advantage, 1st, of multiplying the insertions of the fibres, without increasing the size of the bone, since a concave surface is evidently more extensive than a plain surface would be which should occupy the space between its edges; 2d, of allowing the muscular fibres more room, and consequently giving them greater length than if they arose from an eminence, which also gives more extent to the motions. The pterygoid, digastric cavities, &c. present examples of this arrangement.