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Show 1895.] ANATOMY OP PIPA AMERICANA. 835 of the forearm required by so purely swimming a creature as Pipa, its place having been gradually taken by another muscle more fitted by its place of origin to bring about those movements. A remarkable resemblance between Pipa and Dactylethra is afforded by the peculiar arrangement of the latissimus dorsi muscle in the twTo genera. Dr. Maurer' has described and figured in Dactylethra an " abdominal" portion of the latissimus which is quite as extensive as in Pipa. From the figure (fig. 10) which illustrates this I infer that the transversely running part of the muscle is also present. It is possible, of course, that the resemblance is one due to a similar environment, for Dactylethra is quite as aquatic in its habits as is Pipa. On the other hand, there is some evidence that the likeness is one indicating a deeper-lying affinity; for Maurer points out that in Ceratophrys the abdominal portion of the pectoral is feebly developed, while in Dactylethra it is large as in Pipa; in both of these genera the fore-limbs are largely used, and the fore-limb of Ceratophrys is much stouter than that of Dactylethra; so that on a priori grounds it might be expected that the pectoral of the former would be larger. The same kind of argument might apply to the latissimus, which is the antithetical muscle to the pectoral. There are therefore some grounds for believing that the resemblance between Pipa and Dactylethra in this matter are resemblances of genetic importance. The great extent of this muscle in these two genera of Anurous Amphibians is suggestive of the M a m m a l to which it has been said that the myology of the Anura bears more resemblance than the Urodela. The rhomboideus (or retrahens scetpulce), which in Rana guppyi arises almost entirely from the spines of the vertebrae-a small portion only springing posteriorly from tbe tendinous inscription of the extensor dorsi communis-and not from the transverse processes as in Rana esculenta, is totally absent in Pipa. To the under surface of the scapula are attached three muscles, which Ecker terms the transversi scapulares ; they are all three present in Pipa. So, too, are the levator anguli scapulce, the slernocleido-mastoid, and the protrahens scapulce, which attach the scapula to the head. The infraspinatus arises, as in the frog, from a large portion of the dorsal surface of the scapula; a few fibres, however, take their origin from the fascia which lies between the scapula and the head. In the frog a straight line ruled across the scapula would indicate the sharply marked anterior boundary of the origin of the muscle. In Pipa the corresponding line is V-shaped, the muscle being really in two parts. The anterior half of the muscle, which extends further beyond the edge of the scapula than in Rana, crosses over the posterior portion near to the insertion and narrows rapidly to a thin tendon which is inserted in a line with, but inde- 1 " Die ventrale Eumpfmuskulatur der anuren Amphibien," Morph. Jahrb. 1895. |