156 THE VOYAGE OF H.M.S. CHALLENGER. 



In Arctocephalus it is a triangular muscle and arises from the supraspinous fossa, to within 

 half an inch from the glenoid cavity. Overhanging it upon the anterior border is the episubscapu- 

 laris, separated by a deep furrow. In considering this origin the configuration of the scapula must 

 be grasped. The supraspinous fossa is divided into two by a well-marked ridge, or diminutive 

 spine, anterior to which the suprascapular muscle is thick, whilst posterior it is thin ; at the outer 

 third of the ridge there is a trench between the fibres arising anterior and posterior to it, but no 

 division in the fibres internal to this. From the ridge and the partial trench, it is seen that this 

 muscle is a double one and consists of two parts, an anterior lying in front of the ridge, and 

 a posterior behind it. The anterior part goes to the great tuberosity of the humerus, and is 

 inserted into the capsule over the superior surface of the joint, into the pit on the anterior and 

 upper surface of the upward prolongation of the great tuber, into its upper anterior half and into 

 the posterior surface ; a fasciculus crosses from the great tuber to the tip of the lesser tuber, and 

 is inserted into the outer side of it, forming a narrow muscular bridge over the transverse ligament 

 and the biceps ; it joins the fibres of the pectoral below the great tuberosity. The posterior part 

 lying posterior to the ridge and above the spine is inserted into the pit or impression on the outer 

 side of the great tuberosity, above the pit for the infraspinatus, and into the capsule of the joint 

 superiorly. In Otaria and Tricheehus it has a single insertion. 



Upon the great humeral tuberosity of the young Arctocephalus there are three depressions 

 for tendons, comparable in this respect with the human great tuberosity. In the human subject 

 these are for the supraspinatus, infraspinatus, and teres minor, but in the adult specimens the 

 two lower are fused and the upper and lower extremities of this combined depression are deeply 

 pitted, showing that the fibres going to either end act somewhat independently. As pointed out, 

 the spines of the scapulas in the Phocinee and Arctocephcdi are in very different positions upon their 

 respective bones. The accessory spine or ridge of bone in Arctocephalus bears the same relation 

 to its scapula as the only spine in the Phocinre. The origin of the posterior part of the supra- 

 spinatus in the former, disregarding the spines, is from the same site as the infraspinatus in the 

 latter, and both are inserted into the same part of the major tuberosity. The actions of the 

 posterior part are those of an infraspinatus, so it may be regarded as a transposed muscle ; and 

 the infraspinatus in Arctocephalus is functionally a large teres minor. If the infraspinatus were 

 placed above the spine in the Phocinas, and the spine changed to a lower latitude, then there 

 would be almost the same arrangement of these muscles in both. In the Phocinae it is supplied 

 by the suprascapular nerve from the 6th cervical ; in Arctoccphcdus by the suprascapular. 



In the Phocinte it carries the fore-limb forwards, and in Arctoccplmlus the anterior part 

 raises the fore-limb with the episubscapularis and turns it slightly inwards. The posterior part 

 with the insertion, like the human infraspinatus, is a feeble elevator of the limb, but a powerful 

 rotator outwards, bringing the fore-limb backwards to the side. 



The Infraspinatus lies beneath the deltoid and is similar to it in form. It arises from the 

 posterior border of the spine of the scapula ; from the scapula between the spine, and the origins of 

 the triceps posteriorly, and the deltoid internally. It goes towards the shoulder ; a little beyond the 

 spine its fibres blend with the tendon of insertion of the supraspinatus. Over the dorsum of the 

 neck of the scapula, it is between the supraspinatus and the teres minor. It is inserted into the 

 outer side of the great tuberosity of the humerus ; and into the capsule of the shoulder-joint, 

 lower than the supraspinatus. 



