Book One -- The things that sustain and support the entire body, and what braces and attaches them all. [the bones and the ligaments that interconnect them] | Chapter 4 On the Structural Relationships of Bones

In what ways double joints are formed

The radius (figure 1, chapter 24; or join m in figure 3 to l in figure 5, and p in figure 5 to o in figure 7) is joined to the ulna by a double joint [articulatio radio-ulnaris proximalis et distalis], by virtue of which it is capable only of a simple motion, which is into a prone or supine position. Near the humerus, the ulna admits the capitulum of the radius into a depression [incisura radialis] carved into it, and next to the carpus the hollow [incisura ulnaris] of the radius receives the capitulum of the ulna.


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The same thing is seen in the joint of the calcaneus and the talus [articulatio subtalaris] (if I may for a moment consider ginglymi producing an obscure movement) [facies articularis calcanea posterior]. In its posterior area the talus receives a projection (insert P of fig. 7, ch. 33 into Q of fig. 4 and S of fig. 4 into R of fig. 7) [facies articularis talaris posterior] of the calcaneus, and in the anterior depression [facies articularis talaris anterior et media] of the calcaneus the head of the talus is connected by a joint [articulatio talocalcaneonavicularis], so that with the best justification the bones are said to be articulated here also by mutual entry. The ancients seem also to have placed double articulations in this category, even though they are not made by a mutual entry of different types, but when bones join is a similar manner on both sides, as the connection [articulatio atlanto-occipitalis] of the head to the first vertebra may be judged. For where the two depressions (join B in fig. 1, ch. 15 to N in fig. 2 and D, E, F, G in fig 1 to O, P, Q, R in fig. 2) [facies articularis superior] of the first vertebra are separated from each other, the two heads [condylus occipitalis] of the occipital bone are articulated as if by enarthrosis, and the articulation of the right side differs not at all in type or form from that of the left. The other vertebrae are joined in the same way. The inferior or lower one is connected to the one above by a double joint [articulationes zygapophysiales]; these are the joints which we shall say are at the base of the spine or posterior process of the vertebrae. I am not speaking now of the connection [discus intervertebralis] of vertebrae which they form on their own bodies (R in the figure in Chapter 14), since this varies as far as the present subject is concerned. Thus, as far as the form of articulation is concerned, the vertebrae located above the twelfth vertebra of the thorax are joined together in the posterior joints by arthrodia; but those that lie below the twelfth are joined by a kind of enarthrosis (join O in fig. 2, ch. 14 to K, L, M in fig. 3). But if we include this kind of vertebral joint as ginglymus because they are double (one to each side), we would also admit that certain articulations of this kind [articulatio plana] have not just a simple motion, since besides flexion and extension the vertebrae are moved a little to the sides as well. Yet I do not believe the leading ancient anatomists said the vertebrae were articulated by ginglymus because (with the sole exception of the first cervical and generally the twelfth thoracic) one vertebra is always received in its upper portion by another, and in its lower portion receives the vertebra below; or, on the contrary, that it receives another with its upper portion, and its lower is received. But this is what Galen affirms, 40 saying that ginglymus is made in this way, and perhaps not noticing that if what he claimed were so, three bones would have to meet at the articulation: the first bone would be a vertebra that is received on its upper side, the second a vertebra which receives this upper side, and the third a vertebra which is received by the lower side of the middle or first vertebra (see the three vertebrae, fig. 3, Chapter 19). For one and the same vertebra to receive and be received, it would be necessary to have in addition to that vertebra both a receiving vertebra and one that is received converge upon it. And by this reasoning, ginglymus would have to be applied to a great number of bones: 41 to those which enter another bone with their lower portion, and admit another with their upper; or contrarily, which on their superior surface enter one bone, and receive another on their lower, without respect to the form of articulation. The first bones of the digits (B in fig. 1, ch. 27 and E in fig. 2) would be considered to be of this type; they are joined on their superior surface by enarthrosis to the metacarpal bones, and in their lower portion they enter the hollows of the next digital bone. I shall deal at length in the appropriate place with the joints of the digits and vertebrae; now I shall explain joints showing no motion at all [synarthroses], noting first that no connection of bones so far mentioned is made without the hollows and heads or surfaces being covered by a smooth and slippery cartilage [cartilago articularis], the only exceptions being the connection of vertebral bodies (R in the fig. for ch. 14) to each other and that of the sacrum with the two bones [ossa ilii] joined to it [articulatio sacroiliaca], where you will later hear that cartilaginous ligament 42 intervenes specially. The joints that will now be described, deprived of all motion whatsoever, are never made with a smooth, slippery contact.



Book One -- The things that sustain and support the entire body, and what braces and attaches them all. [the bones and the ligaments that interconnect them] | Chapter 4 On the Structural Relationships of Bones