OCR Text |
Show 1869.] MYOLOGY OF MENOBRANCHUS LATERALIS. 453 but not its caudal portion, consists of distinct muscular layers superimposed. MUSCLES OF THE TRUNK. The external oblique (figs. 3, 4, 8, 9 & 10, Ex. O). The fibres of this muscle extend obliquely backwards and downwards; and the muscle itself forms a sheet of such fibres, which extends from the lateral furrow nearly to the ventral middle line of the body, and from the shoulder to the pelvis. Towards the tail it seems to unite indistinguishably with the internal oblique. The internal oblique. This (as in Menopoma) is the largest muscle of the body, extending, as one may say, from the urohyal to the tail's end. The fasciculi of fibres are rather large and coarse, and extend from one tendinous intersection to another. The direction of the fibres is forwards and downwards. The muscle is partly inserted into the ilium and its rib ; but some fibres pass beneath these hard parts, and the muscle is so continued on into the tail. Towards its anterior insertion this muscle appears to fuse with the rectus (which is superficial to it), and to constitute a sterno-hyoid (figs. 4 & 5, S. H). The transversalis is a delicate muscular layer, extending from the region of the heart backwards to a little behind the pelvis. Rectus (fig. 4, R). This muscle is very delicate and thin in the abdominal region ; towards tbe pectoral arch and in front of it it is thicker, and covers externally the internal oblique, with which it appears to fuse, when they pass forwards as the sterno-hyoid (figs. 4 & 5, S. II) to its insertion into the urohyal. This muscle may be regarded as continued on even to the mandibular symphysis by means of the genio-hyoid (fig. 4, G. H). Retrahente.s costarum. The muscular fibres I thus name run backwards on each side of the spine, being applied to the under surfaces of the bodies and transverse processes of the vertebrae. They extend from beneath the head to tbe pelvic region, but do not go on into the tail. MUSCLES OF THE HEAD. Temporalis (figs. 1, 2, & 3, T). This muscle arises from the middle of the upper surface of the skull, and (by fascia) from the first neural spine, also from the dorsum of the pterygoid and of the small bone extending outwards * in front of the suspensorium and above the pterygoid. From this extensive origin (reaching forwards a little in front of the eyeballs) the fibres converge, and are inserted, by a strong tendon, into the summit of the mandible, just in front of its articulation with the quadratum. Its insertion is posterior and somewhat internal to the insertion of the tendon of the masseter. Pterygoid. I do not find this muscle distinct from the temporal. * See ' Ontleed en dierkundige Bijdragen tot de Kennis van Menobranchus,' by J. Van der Hoeven (Leyden, 1867), pl. ii. fig. 4, i. PROC. ZOOL. Soc-1869, No. XXX. |