OCR Text |
Show 1895.] ANATOMY OP PIPA AMERICANA. 833 comparisons are more difficult. Its insertion on to the stomach reminds us of Prof. Huxley's descriptionl of a muscle in the Crocodile which " arises on each side from the anterior margin of the pubis; and its fibres pass forward, diverging as they go, to be inserted into the ventral face of the posterior part of the pericardium and into the ventral and lateral parts of the fibrous capsule of the stomach." More important is the comparison with the frog, in which there is a muscle embracing the oesophagus, the so-called diaphragm. This is figured by Howes in the ' Atlas of Biology,' and described by Ecker as a part of the conjoined obliquus internus transversus; it arises, however, from the transverse process of the anterior vertebrae, but may still represent the anterior portion of the muscle described and figured here in Pipa. It is, however, perhaps more likely that the diaphragm of Rana is represented by the termination of the obliquus internus lettered a in m y diagram (woodcut, fig. 2) of Pipa. If it be possible to compare the rudimentary diaphragm of Rana with that of the Mammalia, it seems even more possible in the case of Pipa. For in Pipa the diaphragm is formed by a dorsal and ventral set of muscles; there is a complete ring of muscles as in the Mammal. The female frog which I dissected bore a number of young upon her back. I examined one of these, a fully-formed frog of about half an inch in length, in order to ascertain how far the various structures described above were visible. The anterior end of the young frog was cut into a series of longitudinal sections. I found that the lungs hung freely in the body-cavity after their emergence from the thoracic region; there was no trace whatsoever of any muscular or other attachment to the parietes. On tbe other hand, that section of the diaphragm which I have described above as shutting off the heart and pericardium from the abdominal cavity was present. So far, therefore, as one is at liberty to draw inferences from the order of development of various structures, the muscular fascia which spreads out over the lungs is a newer structure and perhaps conditioned by the special needs of Pipa, which is, as is well known, more purely aquatic in its habits than are many other Anurous Amphibia. § Myology. The muscular anatomy of this Amphibian has been to some extent described by Mayer with an illustrative figure. I have endeavoured to supplement his account with some additional details. The animal was dissected side by side with an example of the large Rana guppyi from the Solomon Islands, which agrees in its myology with Rana esculenta, excepting in some small particulars noted in the course of the following description. The English translation by Haslam of Ecker's ' Anatomy of the Frog' has been m y guide in comparing the muscles of the two animals, 1 Ibid. p. 568. |