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Show 1895.] MUSCULAR ANATOMY OF XENOrUS. 845 any marked degree, nearly meet those of the upwardly running " musculus pulmonum proprius." It is evident, therefore, that the " diaphragm " of Xenopus is in complexity markedly in advance of that of Rana and closely resembles that of Pipa. § Myology. I have not attempted even so complete an account of the myology of Xenopus as I have of Pipa, incomplete though that was. I have contented myself with a description of some of the more important muscles which show variations in different types, and from which therefore it m ay be possible to draw conclusions as to affinities with the very few types of Anurous Amphibians whose myology is known. I have principally made use of Dr. Haslam's translation of Ecker's ' Anatomy of the Frog'l as the basis of m y comparisons; but I have dissected all the muscles referred to in a specimen of the large Solomon Island Frog, Rana guppyi. The Rectus abdominis is a broad muscle which arises not only from the extremity of the pubis but also from the fascia of the thigh, as shown in the accompanying illustration (woodcut fig. 3 ) ; possibly, however, the muscle only arises from the cartilaginous plate at the end of the pubis (the prepubis), as I cannot distinguish any distinct line of demarcation between it and the adjacent obliquus internus. The fibres pass forward and diverge beneath the end of the sternum into the two recti, which are inserted underneath tbe sternum. Obliquus internus. A s has been just mentioned, this muscle appears to be quite continuous with the last; but as a portion of the entire muscle underlies the obliquus externus and gives off a branch to the lung, it must, I think, be regarded as obliquus internus. It will perhaps be in accord with convenience to regard that portion of the entire muscle which springs from the fascia covering the thigh as referable to the obliquus internus. In m y account of the myology of Pipa americana, I have referred to a remarkable muscle which I termed the "pectoro-mandibular," as descriptive of its origin and insertion. I find in Xenopus underlying the mylohyoid a mass of muscle which seems to correspond to this, though its insertions are different. It is, in fact, in Xenopus to be regarded as a portion of the deltoid, for its fibres run alongside of other fibres which arise from the clavicle and from the tip of the sternum, and are inserted upon the humerus with the rest of the deltoid ; it forms, in fact, the clavicular head of the deltoid. The Depressor mandibular arises, as in Rana esculenta, from the fascia covering the back, and is in actual contact with the anterior of the latissimus dorsi. The dorsal sheet of muscle formed by these two completely covers over the underlying infraspinatus. The Latissimus dorsi consists not only of a portion corresponding to the same muscle in the C o m m o n Frog, but of a larger posterior 1 Clarendon Press, 1889. PROC. ZOOL. Soc.-1895, No. LIV. 54 |