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

E)na/rqrwsij: Enarthrosis 26

Enarthrosis denoted that type of articulation in which the cavity or hollow of the receiving bone is deep, carved out like a vinegar-cup or acetabulum. The swelling head that articulates with it, as well as the hollow itself, are simple in this variety of articulation: a single hollow and a single head, just as we see occurs in the articulation of the femur with the hip [articulatio iliofemoralis], the humerus with the scapula [articulatio glenohumeralis], and the metacarpal and metatarsal bones with the first bones of the digits [ossa digitorum]. These joints are given many visible motions. The femur and the arm bone, 27 which we call the humerus, are flexed, extended, moved sideways, and rotated. The first bones of the digits [phalanx proximalis] are not rotated, 28 which you will hear happens not only because of the arrangement of the muscles and sesamoid bones but also because of the construction of the joint [ginglymus]. The carpus is joined to the radius by this kind of joint: it is flexed, extended, and moved sideways. The radius is joined to the humerus [articulatio humeroradialis] by enarthrosis, because of which it is capable of even more movements; it is flexed and extended together with the ulna, and then rotated [articulatio trochoidea], so that it is agreed that in simple joints which are constructed with a continuous and uninterrupted coating (so to speak) of cartilage, Nature devised enarthrosis whenever it seemed best to her that the bone be moved with many motions,


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using in those motions the simplest possible and least complex connection of the bones. To such a bone, the navicular, a head [caput tali] (join O in figure 3 Chapter 33 to k of figure 11) is joined by this type of articulation. 29 When we discuss them, we shall also show that certain carpal bones (figure 2 Chapter 25, joint of no. 7 to 1) are joined by this means; similarly, the cartilages of the second, third, fourth, and fifth ribs are joined to the sternum by this type of articulation [articulatio plana]. For the time being it is enough to explain the varieties of joints and their character, and to consider in them the intention of the Maker, adding only such examples as these latter ones to be counted among those having obscure motions. For to enumerate all the joints every time, easy as it would be for me to do, would encumber the beginner in anatomy with bones not yet explained, and the difficulty of the task would deter him from the fairest investigation of the works of God.



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