| OCR Text |
Show 278 MR. F. G. PARSONS ON T H E [Mar. 20, ribs from about the 9th to the last: there are thus two distinct layers of fibres running in opposite directions in the dorsal region. The variations that are met with consist of more or less complete suppression of these parts. In Dasyprocta and Cavia cobaya, for example, tbe posterior part is wanting and the anterior well developed, so that in the former there is a continuous layer of muscle, the fibres of which run in the same direction, stretching from the 4th to the 13th rib. In Sphingurus, on the other hand, each part is equally diminished, so that there is a space between them resembling the arrangement in Man. In the Dipodidae the muscle is almost entirely represented by fascia. Among the other animals examined Ceredon and Pteromys resembled Aulacodus, while Ccelogenys, Arctomys, and Xerus had the arrangement found in Dasyprocta. Octodon resembled Sphingurus, but was remarkable for having the posterior part of the muscle better developed than the anterior. Sacro-lumbalis.-This muscle has the usual attachments. It is continued forwards by the accessorius, the limits of which are indistinguishable. This is succeeded by the cervicalis aseendens, which is attached to the transverse processes of the posterior three cervical vertebrae, except in Dasyprocta and Ccelogenys, where it only goes to the last two. Longissimus Dorsi.-This muscle, as well as the semispinalis and multifidus, has the usual arrangement: their exact attachments vary with the number of vertebrae. Transversalis Capitis and Colli.-When both these muscles are present they are continuous. The latter is attached to the transverse processes, except sometimes the first and often the last one or two. The transversalis capitis or trachelo-mastoid is attached to the base of the paroccipital process, except in Castor, where it goes to the base of the mastoid process. It is present in all the Sciuromorpha, as well as in the Octodontidae, Hystricidae, and Dasyproctidae. In the Caviidae it is present in Ceredon, but absent in Cavia cobaya. In the remaining families the muscle was not examined. Splenius Capitis et Colli.-The splenitis capitis is always present, and has the human attachments and relations. The splenius colli was found in the Dasyproctidae, where it was inserted into the anterior three transverse processes in Dasyprocta and into the transverse process of the atlas only in Ccelogenys. A small slip representing this muscle was found in Myopotamus, but in no other animal was it seen. Complexus.-This muscle has the usual attachments. It shows signs of being divided longitudinally into two parts ; of these the outer is inserted by tendon and the inner by flesh. In some of the Hystricomorpha a slight tendinous intersection was seen in the inner part, reminding one of the biventer of M a n ; but this arrangement was not seen in the Sciuromorpha, except in Castor, |
