İKİNCİ FEN · İKİNCİ BÂB · ÜÇÜNCÜ FASIL · Birinci Madde
Article One
It describes the bones of the arm.
O Noble One! Know that anatomists have said: The bone of the arm is created in a cylindrical form, so it remains safe from harm, its upper portion being convex and entering a loose joint within the shoulder socket. This looseness causes dislocations to occur frequently. There are two benefits to this looseness: fulfilling needs and moving with ease and safety. Fulfilling needs is that this joint can move freely in all directions. Safety and protection are of two kinds: for although the joint moves around it, these movements are not so forceful or numerous as to cause damage or dislocation. Thus, there is no fear of its ligaments weakening and loosening. Perhaps the arm remains mostly still and motionless while the joints of the hand are active. Therefore, the joints of the hand are created more firmly than the joint of the arm.
Four ligaments secure the arm joint. One is a transverse membrane which, like other joints, encircles the joint completely. Two descend from its posterior aspect; one of these is broad and flat, adhering to the ulnar side in this manner. The other is larger and more robust, descending with the fourth ligament from the coracoid process. Their forms are flattened and touch the arm bone.
The arm bone creates a lateral hollow on its lower surface and a lateral prominence on its upper surface. Thus, the muscles, nerves, and vessels that gather and arrange themselves upon it are covered and embrace what they surround, allowing the two hands to reach each other comfortably. Two contiguous protrusions arise on the lower aspect of the arm bone; the one on the inner side is long and slender. It has no articulation with any object but is created to protect nerves and vessels. The protrusion on the outer side, along with the hollow in the elbow and the condyle within that hollow, complete the elbow joint. Between them there is a notch, and two hollows are found on either side of it; the upper hollow is anterior, the lower hollow posterior. However, the upper hollow has no obstruction; it is smooth and uniform on all sides. The second hollow above, however, is larger, and the region near the lower hollow is not flat, nor is the hollow circular, but created straight and true like a membrane. Thus, when the radial prominence of the forearm moves laterally towards it, it comes to rest there. These two hollows are called thresholds. The joints here are arranged in this manner.