OCR Text |
Show 1905.] ANATOMY OF THE LEATHERY TURTLE. 297 muscular, and in front form a rounded tendon that runs forward above the transverse process of the last cervical vertebra towards the anterior cervical vertebrae. Its insertion was, unfortunately, not seen. Posteriorly, this mass is attached partly to the second rib, partly to the sides of the second dorso-lumbar vertebra, and partly goes on directly above the neck of the second and succeeding ribs. Part a (interspinales) in this region forms a definite strand of muscle running between the spines of the last cervical and first two dorso-lumbar vertebrae. These degenerate muscles could not be followed beyond the sacrum, owing to injury of that part, but behind the ninth rib they showed no signs of diminution, so that probably, as in very young animals, they passed on over the sacrum. In Chelonia in general these muscles terminate from the second to the eighth ribs in the adult, while the interspinales are entirely lost.A s regards these muscles, therefore, Dermochelys is less specialised than the rest of the Chelonia. And as the degeneration of the back-muscles is due to the immobility of the carapace, we may infer that the relative softness of the carapace in Dermochelys is a primitive condition-a stage in the development of a true carapace, and not a secondarily acquired softness brought about by retrograde modification of a hard carapace. Muscles of the Shoulder Girdle and Fore Limb. Cotto-scapularis (text-figs. 55 & 60. 40).-Origin : from the lateral parts of vertebrae in., iv., v., vi., v i i . Insertion: upon the median border of the scapular fossette and upon the median surface of the head of the scapula. This muscle is separated by the roots of the brachial plexus into four layers. The insertion does not agree with that given by Fiirbringer for Sphargis and Chelone. Another muscle (text-figs. 55 & 59. 40 a), which I cannot very satisfactorily identify, may possibly be part of the collo-scapularis. It takes origin from the lateral parts of the second vertebra in forward continuation of the preceding muscle, and is inserted upon the upper end of the scapula just dorsal to the insertion of the posterior part of the sphincter colli. Testo-coracoideus (text-figs. 55, 57, 58, & 60. 42).-Origin : the plastron, along a line that runs diagonally forward and outward along the posterior edge of the outer part of the origin of the pectoralis, and thence passes behind the arm to the carapace and along the anterior border of the second rib to the hinder margin of the scapular fosette. The origin from the plastron is fleshy, from the border of the rib tendinous. Insertion : fleshy, to the deep surface of the posterior half of the inner end of tbe coracoid, and by thin tendinous aponeurosis along the coraco-clavicular ligament and down the inner border of the scapula very nearly to its dorsal end. |