I have made an experiment which shows very evidently the identity of the tendons with these aponeuroses; it consists in macerating for some days a tendon; it then becomes supple; its fibres separate; by stretching in the direction of its width, it forms a kind of membrane which it would be impossible to distinguish from a true aponeurosis. _Aponeuroses of Insertion in the form of an Arch._ They are much more rare than the preceding. When a great vessel passes under a muscle, nature employs this means, so as not to interrupt the insertion of the fleshy fibres. The diaphragm for the aorta, the solæus for the tibial artery, exhibit an arrangement of this kind. The insertion is made on the convexity, and the passage of the vessel under the concavity of the arch, both extremities of which are fixed in the bone. It has been thought for a long time that the arteries could be compressed under these arches; and hence the explanation of popliteal aneurisms, of apoplexy by the reflux towards the head of the blood interrupted in the aorta, &c. But it is very evident that by contracting, the fleshy fibres would enlarge the passage, instead of contracting it, since the necessary effect of these contractions is to enlarge in all directions the aponeurotic curve, an effect which would be directly opposite, if their insertion was made at the concavity. These aponeuroses are strongly interlaced and very resisting. _Aponeuroses of Insertion with Separate Fibres._ They are a collection of an infinite number of small fibrous bodies wholly distinct from each other, which seem to be detached from the periosteum, as the threads of velvet go off from their common woof. Each is continuous with a fleshy fibre; so that when by maceration we remove all those fibres, these small bodies become floating and are seen perfectly well, especially when the periosteum which has been detached is plunged into water. It is evident that this mode of insertion on the part of the muscles requires always broad osseous surfaces, since each fibre has a place of its own; we have an example of it in the superior part of the iliacus, of the anterior tibialis, of the temporal, &c. If all the muscles were inserted in this manner, ten times more surface in the skeleton would not be sufficient to receive them. ARTICLE NINTH. OF THE TENDONS. The tendons are a kind of fibrous cords, intermediate to the muscles and the bones, transmitting to the second the motion of the first, and performing in this function a part wholly passive. I. _Form of the Tendons._