OCR Text |
Show 416 MR. A. SANDERS ON THE [June 9, Infraspinatus arises from the whole upper border of the scapula proper in a semicircular manner ; a few of tbe anterior fibres arise from the internal surface of the bone ; the fibres converge, and are inserted into the outside of the humerus beyond its head, dorsad of the insertion of deltoid, tbe interior part of the insertion being between the insertions of the two last muscles. This appears to correspond with the infraspinatus, by the same line of argument; if the coracoid points to the supraspinous fossa, the scapula would point to the infraspinous fossa. Mr. Mivart has called it the second part of the deltoid; but in this animal it has a separate insertion from that muscle. In addition the above arguments in favour of this view, I would draw attention to tbe arrangement of the insertions of these three muscles, which correspond in a striking manner with the arrangement of the three analogous muscles in mammals. Biceps is represented only by the coracoid head. It arises, broad and fleshy, from the anterior and inner half of the articular border of the coracoid, and from the surface of bone behind it. In passing over the shoulder-joint it developes a broad thin tendon ; beyond that point it again becomes fleshy, and in the arm it is thick and round ; it is inserted by a narrow tendon into the upper part of both radius and ulna, in conjunction with and on the distal side of the insertion of brachialis anticus. Coraco-brachialis brevistixises broad and fleshy dorsad of the last, from the posterior and inner half of the articular border of the coracoid, and from the surface of bone outside it; passing close under the humero-scapular articulation, it is inserted into the inner side of the shaft of the humerus for nearly two-thirds of its length. Coraco-brachialis longus arises behind this, from the posterior angle of the coracoid bone, and, passing down inside the arm, it is inserted, narrow, into surface of bone immediately above the inner condyle of the humerus. Brachialis anticus arises from the whole length of the flexor surface of the humerus, commencing beyond the insertion of the supraspinatus, and is inserted entirely into the proximal part of the ulna, together with part of the biceps-tendon. Trapezius consists of two portions, united together by a thin layer of muscular fibre. The anterior portion arises from the side of the complexus in conjunction with the neuro-mandibularis; the posterior part is attached to the general aponeurosis covering the dorsal muscles, extending back as far as the fourth dorsal vertebra: this part is inserted into the scapula immediately dorsad of the claviculo-scapular articulation ; the anterior part is inserted into the upper third of the clavicle. Latissimus dorsi arises from the spinous processes of the vertebrse, from the seventh, or last but one, cervical to the fourteenth dorsal, both inclusive ; the anterior fibres are directed straight downwards, and the posterior obliquely downwards and forwards, to be inserted into the upper surface of the humerus, occupying one-third of its extent beyond the head. Triceps has four origins, the outer section arising by two heads, one |