The two prominences, which we have just described from a general point of view, present special arrangements which it is necessary to point out. When we examine the form of the outline of the inferior extremity of the humerus in man, the bear, the cat, the dog, the ox, and the horse, we find in following this order that the extremity tends to become narrow transversely, and that the epicondyle and the epitrochlea are less and less prominent on the external and internal aspects respectively. These two processes, indeed, project backwards; the epitrochlea always remaining more developed than the epicondyle. Because of this projection backwards, the cavity situated on the posterior surface of the inferior extremity, the olecranon fossa, is very deep, more so than in the humerus of man. Its borders being thus formed by the two processes, are very prominent. In front we find the coronoid fossa, which is less deep than that of which we have just spoken. There exists in some mammals an osseous canal, situated above the epitrochlea, and known as the _supratrochlear canal_ (Fig. 19). It is bounded by a plate of bone which at its middle portion is detached from the shaft of the humerus, and blends with the latter at both its extremities. The brachial artery and median nerve pass through the foramen. [Illustration: FIG. 19.--INFERIOR EXTREMITY OF THE LEFT HUMERUS OF A FELIDE (LION). 1, Epitrochlea; 2, supra-epitrochlear foramen.] [Illustration: FIG. 20.--INFERIOR EXTREMITY OF THE LEFT HUMAN HUMERUS, SHOWING THE PRESENCE OF A SUPRATROCHLEAR PROCESS. 1, Epitrochlea; 2, supra-epitrochlear process.] A similar condition is sometimes found, as an abnormality, in man, which presents itself under the following aspect (Fig. 20): an osseous prominence more or less long, in the shape of a crochet-needle--supra-epitrochlear process--situated 5 or 6 centimetres above the epitrochlea; the summit of this process gives attachment to a fibrous band, which is inserted by its other end into the epitrochlea and the internal intermuscular aponeurosis. The fibro-osseous ring thus formed gives passage to the brachial artery and the median nerve, or in case of a premature division of this artery to the ulnar branch of the same.[9] [9] For further details of this anomaly, see Testut, 'The Epitrochlear Process in Man' (_International Journal of Anatomy and Physiology_, 1889); A. Nicolas, 'New Studies on the Supratrochlear Process in Man' (_Review of Biology of the North of France_, t. iii., 1890-1891). There is also found in some mammals a perforation of the thin plate of bone which, in others, separates the olecranon fossa from the coronoid. This perforation is sometimes found as an abnormality in the human humerus.