We have previously pointed out that in the carnivora this muscle is visible on the internal and posterior aspects of the forearm, in the interval which is limited in front by the flexor carpi radialis and behind and outside by the anterior ulnar. Certain details are still to be added to the description of this muscle. We will enter on an analysis of them after we have given some indications relative to the following muscle: =Deep Flexor of the Digits= (_Flexor digitorum profundus_) (Fig. 75, 21, 22; Fig. 76, 12; Fig. 77, 11, 11).--This muscle is covered by the superficial flexor. It arises from the epitrochlea, from the radius, and from the ulna, either from the olecranon process--as in the ox, pig, and horse--or from almost the whole extent of the shaft of the same bone, as in the cat and dog. [Illustration: FIG. 78.--LEFT ANTERIOR LIMB OF THE HORSE: INTERNAL ASPECT. 1, Internal flexor of the metacarpus or great palmar; 2, inferior part of the biceps; 3, inferior part of the brachialis anticus; 4, internal lateral ligament of the elbow; 5, pronato teres muscle.] The radial fasciculus represents in the domestic quadrupeds the long proper flexor muscle of the thumb in man. For this reason we shall describe the muscle afresh in the following paragraph: The fleshy bundles of which we have just spoken terminate in a tendon which afterwards divides into slips, the number of which is in proportion to the digital division of the hand. These slips then pass through the slit or _buttonhole_ in the tendon of the superficial flexor, and proceed to terminate on the third phalanx; hence the name of _perforating_, which is also given to the deep flexor of the digits. In the dog and the cat the tendon is divided into five portions, each of which proceeds to one of the digits. The internal tendon, which is destined for the thumb, terminates on the second phalanx of this digit. In the pig the tendon divides into four tendons destined for the four digits. In the ox there are but two tendons. In the horse the tendon is single. As their names indicate, these muscles, both superficial and deep, flex the digits. In addition to this, they flex the hand on the forearm. We mentioned above that certain details relative to the superficial flexor must be analyzed in a special way. We now add that this should also be done with regard to the deep flexor. The point in question is the arrangement which the tendons of these muscles present at the level of the palmar region of the hand. It is easy, in the case of the dog or the cat, to picture to one's self this arrangement, especially if we recollect that which exists in the human species. The tendons of the flexors are placed on a kind of muscular bed formed by the union of the muscles of the region, but, moreover, from the point of view of external form, these tendons are not of very great importance.