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Show 280 MR. P. G. PARSONS ON THE [Mar. 20, In Lagostomus, Hystrix, and Sphingurus the muscle, on careful dissection, was found not to be continued forwards to the first rib with the rectus. In Arctomys it went not only to the first rib, but also to the junctions of the 2nd, 3rd, and 4th with the sternum. Interned Oblique and Transversalis.-These muscles are closely blended, requiring careful examination to make out their separate attachments. The internal oblique rises from the lumbar fascia, the crest of the ilium, and a large part of Poupart's ligament. The fibres run forwards and inwrards to a few of the posterior ribs and to the linea alba. At the abdominal ring a muscular pouch* representing the cremaster supports the testis. There is usually more aponeurosis ventrally than in the external oblique. The transversalis rises from the inner surfaces of a large number of the posterior ribs, from the lumbar fascia, from the iliac crest, and from the outer part of Poupart's ligament, and is inserted into the linea alba, passing deep to the rectus in its whole extent. In Aulacodus, Octodon, Dasyprocta, Cavia cobaya, and Sciurus the muscles are practically inseparable, but in Dasyprocta a white line was noticed running downwards and backwards from the cartilage of the last false rib to the outer edge of the rectus, which appeared to mark the place where the internal oblique became aponeurotic. In Lagostomus the internal oblique becomes aponeurotic near the edge of the rectus, forming a linea semilunaris. It passes superficial to the rectus, while the transversalis remains fleshy and passes deep to it. In Hystrix, Sphingurus, Ccelogenys, and Arctomys the muscles are more separable, and the internal oblique rises from the outer three-quarters of Poupart's ligament as well as its other origins, and is inserted into the posterior ribs-into three in Hystrix, five in Sphingurus, and six in Ccelogenys. Rectus Abdominis.-The rectus arises by one head from the ventral surface of the symphysis pubis and runs forwards between the internal oblique and transversalis, with which it is closely blended, to the ventral surface of the first rib near its junction with the sternum; it is also inserted into the succeeding four or five costal cartilages at their sternal ends by small slips. It has already been noticed that the external oblique is usually continued forwards with it. In Sphingurus it only reaches as far forwards as the second rib, The lineae transversa? are very feebly marked; they are usually five or six in number, but in Arctomys only three could be made out. The Octodontidae are remarkable for having a well-marked decussation of the two recti close to their origin; this has been pointed out by Owen1 and Dobson2 in Capromys foumieri and C. melanurus, as well as by Martin in Myopotamus3 and Octodon4. 1 P. Z. S. 1832, p. 68. 3 P. Z. S. 1835, p. 176. a P. Z. S. 1884, p. 234. * P. Z. S. 1836, p. 72. |