| OCR Text |
Show 1894.] MYOLOGY OP RODENTS. 279 in which, moreover, the inner and outer halves of the muscle were very distinct. Intercostals and Triangularis Sterni.-These muscles have nothing remarkable in their attachments : the latter usually rises from the posterior 4 or 5 pieces of the sternum. Tail-Muscles. The following muscles can be identified :-Extensor caudae, externus and internus ; Abductor caudae, externus and internus ; Flexor caudae, externus, internus, and profundus. With the following exceptions these muscles correspond to Meckel's general description of the tail-muscles of mammalsl:- The abductor caudae internus rises from one transverse process and arches over to the next but one, passing dorsal to the intermediate transverse process. The abductor caudae externus in Myopotamus does not rise from the tuber ischii, its usual origin, but from the pelvic fascia by the side of the lower part of the rectum. In Sphingurus the ischial origin of this muscle is very well marked, as are also all the tail-muscles. In the flexor caudae internus the most internal of the superficial tendons are inserted first, the deeper tendons coming to the surface round the outer side of these. In the flexor caudae externus the most external tendons are first inserted, and the deeper ones reach the surface round tbe inner side of these. Tn Castor a series of fleshy bellies rose from the articulations of the chevron bones to the caudal vertebrae; these soon became tendinous and ran backwards and outwards to be lost in the fat over the transverse process of the next vertebra but one. Each tendon was perforated by the one behind it. Obliquus Externus Abdominis2.-This muscle rises by fleshy digitations from a large number of the posterior ribs, generally about two-thirds of the total number, as well as from the lumbar aponeurosis. The fibres pass downwards and backwards to be inserted into the crest of the ilium, from which they pass across as Poupart's ligament to the anterior part of the body of the pubes. The next fibres are separated from these by a large triangular gap, the external abdominal ring, and are inserted into the anterior part of the body of the pubes. The fibres anterior to these pass ventral to the rectus to reach the linea alba. In the anterior part of the abdomen the fibres blend with those of the rectus, and in some cases are continued forwards with that muscle to the first rib. The intercolumnar fibres over the ring are well marked and form a pouch for the testes. There is very httle aponeurosis near the hnea alba, the most tendinous part being at Poupart's ligament. 1 Traite" general d'Anatomie compare e, p. 175. 2 Owing to the fact that many of the animals I dissected had been eviscerated before they came to me, m y observations on the abdominal muscles are not so complete as I could have wished. 19* |
