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Show 1896.] MYOLOGY OF RODENTS. 177 Sacro-lumbalis and Longissimus Dorsi.-These muscles show nothing remarkable in their attachments. Transversalis Capitis et Colli.-In Mgoxus the trachelo-mastoid or transversalis capitis was absent, in all the other animals both muscles were found. Splenius Capitis et Colli.-The splenius capitis rises from the ligamentum nuchae nearly as far forward as the occiput, and almost entirely covers the complexus; it has the usual attachments. The splenius colli was not seen at all. Complexus.-There is usually a slight tendency to longitudinal division, but this is not seen in Georychus, Bathyergus, Myoxus, or Myodes. Cricetus shows two intersections extending across the whole muscle, while in Rhizomys they only extend across the outer half of it. Tail-Muscles.-In those animals which have tails, the arrangement of the muscles is the same as in other Rodents. Obliquus Externus Abdominis.-This muscle usually rises from the posterior nine or ten ribs. The description already given of it in the other Rodents applies to the Myomorpha, with the exception that it never runs upward to the first rib with the rectus. The outer pillar of the abdominal ring is large and muscular, and is inserted into the whole length of the body of the pubes, external and parallel to the symphysis. The inner pillar is thin and fascial. In Cricetomys five or six lineae transversa were seen extending across the muscle from the rectus, while in Microtus the same thing was also noticed, but much less distinctly. Obliquus Internus and Transversalis.-These muscles can be separated with great care. In Bathyergus they are very well marked, and in that animal the relation of the aponeurosis to the rectus can be made out, and is found to be as in Man. In Mus rattus the scrotal pouches are very large, and are composed entirely of the internal oblique. Rectus Abdominis.-In all the specimens of the family of Muridae examined there was a decussation resembling that already described in the Octodontidae1; this was not seen in Myoxus, Georychus, or Bathyergus, though it was found in Rhizomys. Supracostalis.-In no Rodent was this muscle seen. Psoas Parvus.-The psoas parvus was present in all the specimens except the Gerbille; in Microtus, Rhizomys, and Georychus, however, it w7as small. Psoas Magnus and Iliacus.-These muscles have the usual rodent attachments. Quadratus Lumborum.-In most of the Myomorpha the quadratus lumborum does not seem to rise from as far forward in the dorsal region as it does in the other Rodents. It is attached toall the lumbar vertebrae except in the case of Rhizomys, where it only comes from the first three. 1 P.Z.S. 1894, p. 286. PROC ZOOL. Soc-1896, No. XII. 12 |
