And yet, in the cat and the dog, it is also able to adduct the first metacarpal bone. It must be understood that this movement would be abduction, if the hand could be placed in the position of complete supination, as in the human species. =Long Extensor of the Thumb= (_Extensor secundi internodii pollicis_) =and Proper Extensor of the Index= (_Extensor indicis_).--These two muscles are blended together by their fleshy bodies, so that the single name of _proper extensor of the thumb and index_ is preferable. This muscle is but of slight importance from our point of view, for it is extremely atrophied, and so much the more as the number of the digits is lessened. It arises, as the preceding, from the skeleton of the forearm, and there it is deeply placed. Below, towards the carpus, its tendinous part becomes superficial, to end in the following manner: In the carnivora, the tendon divides into two very slender parts, which are inserted into the thumb and the index. In the pig, the tendon is blended with that of the common extensor of the internal digits. Finally, in the ox and the horse, it is sometimes regarded as being blended with the common or anterior extensor of the phalanges. But to us it appears more rational to say that it does not exist, which, moreover, is explained by the digital simplification of the hand. Internal and Posterior Region =Pronator Teres= (Fig. 76, 8).--This muscle, as may easily be understood, undergoes, as do the supinators, a degree of degeneration in proportion to the loss of mobility of the radius on the ulna. In animals in which the bones of the forearm are not fused it exists; in those, on the other hand, in which this segment has become simply a supporting column, it is not developed--at least, in a normal manner. It is, consequently, found best marked in the dog and the cat. Forming, as in man, the internal limit of the hollow of the elbow, the pronator teres has a disposition analogous to that which characterizes the corresponding muscle in the human species. It arises from the epitrochlea (internal condyle), proceeds downwards and outwards, and is inserted into the middle portion of the body of the radius. It is into the hollow in front of the elbow, which this muscle contributes to limit, that the biceps and the brachialis anticus dip. In the pig and the ox it is atrophied. In the horse it does not exist. We may, however, sometimes find it, but in an abnormal form. We were able to demonstrate its presence in the form of a fleshy tongue situated on the internal side of the elbow (Fig. 78) in a horse which we dissected many years ago in the laboratory of the School of Fine Arts. Moreover--and the fact seemed to us an interesting one--the forearm to which the muscle belonged had an ulna of relatively considerable development (Figs. 79 and 80).[29]