=Teres Minor= (Fig. 72, 9).--This muscle, also called in veterinary anatomy _the short abductor of the arm_, arises from the posterior border of the scapula (the external border in man), and is inserted below the great tuberosity of the humerus, between the attachments of the infraspinatus and deltoid. It is covered by the deltoid and the infraspinatus. =Teres Major.=--This muscle is known to veterinarians as _the abductor of the arm_; it arises from the postero-superior angle of the scapula (the inferior angle of the human scapula), from which it passes to be inserted into the internal surface of the humerus. It is covered by the latissimus dorsi and the posterior muscular mass of the arm. In brief, for the better understanding of the relations of the teres major and minor muscles in quadrupeds, we may fancy the corresponding muscles in man modified in the following manner: The infraspinatus, thicker, covering the teres minor; latissimus dorsi, more extended in its superior part, covering a large proportion of the teres major. As to the relations of the teres minor with the deltoid, they exist in man, seeing, in this case, the same muscle is, in its external portion, covered by this latter. With regard to the relations of the teres major with the posterior muscular mass of the arm, they also exist in man, since the external surface of this muscle is covered by the triceps. These modifications are sufficient to render the small and large teres muscles completely invisible in the superficial layer. The muscles of the shoulder which we have just been studying fulfil, with regard to the articulation which they surround, the function of active ligaments. This rôle is made necessary by the laxity of the scapulo-humeral capsule--a laxity which renders it incapable by itself of maintaining the bones in contact at this joint. The same condition exists in man. =Panniculus Muscle of the Shoulder.=--This thin muscle covers, as its name implies, the region of the shoulder, and is the continuation forward of the panniculus muscle of the trunk. It arises, by its superior part, from the region of the withers and from the superior cervical ligament; thence its fibres descend directly towards the elbow, to terminate at the level of the region of the forearm. The muscle is not found in the pig or in the carnivora. Muscles of the Arm We should remember, at the outset, that in man the muscles of the arm are divided into two groups: one anterior, which contains the biceps, brachialis anticus, and the coraco-brachialis; the other, posterior, which is constituted by a single muscle, the triceps. In animals, we find them in the same number and arranged in analogous fashion--that is to say, in two groups--with respect to the bone of the arm. But then we find that they have undergone a transformation with regard to their length, and it is the change of general aspect which results from this modification that we proceed to examine.