In the ox, the same muscle is divided into two bundles: the internal proceeds to the internal toe, the external is common to the two toes.
In the horse, the tendon of the anterior extensor of the phalanges is divided into two parts of unequal bulk. The smaller of these tendinous slips, which is the more external, unites at the level of the superior part of the metacarpus with the tendon of the muscle which we are about to study in the following paragraph ([Fig. 75], 16). The larger, after having reached the anterior surface of the digit, is attached to the anterior aspect of the first and second phalanges, and then forms a terminal expansion which is inserted into the pyramidal eminence of the third.
At the level of the first phalanx this tendon receives on each of its lateral aspects a strengthening band, which proceeds from the terminal extremity of the suspensory ligament of the fetlock,[26] and crosses obliquely downwards and forwards over the surface of the first phalanx to join the extensor tendon ([Fig. 75], 12).
[26] See [p. 200] for a description of this ligament.
A similar arrangement is found in the ox.
This band is noticeable under the skin which covers the lateral aspects of the ham.
As the name indicates, this muscle extends the phalanges, one upon the other. It also contributes to the extension of the hand, as a whole, on the forearm.
Extensor Minimi Digiti ([Fig. 73], 10; [Fig. 74], 15, 16; [Fig. 75], 14, 15).—This muscle, the lateral extensor of the phalanges of veterinary anatomy, situated on the external surface of the forearm, behind the common extensor of the digits, arises, as a rule, from the epicondyle (dog, cat), or from the external surface of the superior extremity of the radius (horse). The tendon succeeding to the fleshy body appears towards the lower third of the forearm, and at the level of the wrist lies in a groove analogous to that which in man is hollowed out for the passage of the corresponding tendon at the level of the inferior radio-ulnar articulation. This groove corresponds to the same articulation in animals in which the ulna is well developed, such as the dog and the cat; but it belongs to the radius when the inferior extremity of the ulna does not exist—for example, in the horse. Indeed, in this animal the groove in question is found on the external surface of the carpal extremity of the radius.
In the dog, the tendon is divided into three parts, which, crossing obliquely the tendons of the common extensor of the digits, pass to the three external digits, to be inserted by blending with the corresponding tendons of the latter into the third phalanges of those digits.
Thus is explained the name of common extensor of the three external digits which is sometimes given to this muscle.