| OCR Text |
Show 1867.] MYOLOGY OF IGUANA TUBERCULATA. 771 The lateral superficial margins of the muscle are indistinguishably blended with the external oblique, which sends oblique tendinous fibres right across the superficial surface of the rectus. External oblique. This muscle seems to consist of three parts*:- (1) The most superficial portion arises by tendinous interdigita-tions with the dorsal extensor muscles, from the last cervical and all the thoracic ribs. It is a very delicate layer, and ends below by blending with the upper margin of the rectus, with which it becomes inseparably united. It is also inserted (by a tongue of muscular fibres) just above the very strong tendon of insertion of the third portion. It has five tendinous intersections. (2) The second part arises, beneath the first, by less marked digitations from all the thoracic ribs. Passing downwards and backwards, its most anterior portion is strongly inserted into the fifth thoracic rib; elsewhere it ends in a delicate aponeurosis, which is connected with the sixth thoracic rib, and blends with the inner surface of the first or most superficial layer of the muscle. (3) The third part of the external oblique (fig. 1, E. O., and fig. 13, Ex. oi) arises from the posterior surface of the last thoracic rib and from the lumbar fascia. It is inserted, by a very strong tendon, into the spine of the pubis. This muscle appears to continue backwards the upper, or external, intercostals. The internal oblique is of great extent, lining the whole of the thorax. It arises from the inner surfaces of all the thoracic ribs, beginning by a tendinous aponeurosis which is attached to them along a line nearly corresponding to the outer edge of the dorsal extensor muscular mass. It also takes origin from the lumbar fascia just behind the third part of the external oblique. It is inserted by muscular digitations into the inner surfaces of the sternal ribs and (in the abdomen) into the margin of the rectus. This muscle is evidently not continuous with the internal (or sternal) intercostals, as these are superficial to the fleshy insertions of the internal oblique, the fibres of which, moreover, run more parallel to the sternal ribs themselves than do the fibres of the internal intercostals. Transversalis. This muscle is also very extensive, arising by a fascia extending from the pelvis to the last but one cervical rib. Indeed the fascia is continued on into the neck, where it passes beneath the nerves of the brachial plexus, which are external to it, like the abdominal nerves which pass between it and the internal oblique. It is inserted into the border of the rectus and the inner sternal part of the thorax. Internal intercostals. These extend between the sternal thoracic ribs, reaching vertically to the vertebral ribs, and underlying for some distance the external intercostals. External intercostals. The external ones extend between the cervical ribs, as well as those of the trunk. In the thorax they only * Stannius considers that the external oblique and internal oblique each consist of two layers (loc. cit. p. 104). |
