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Show 1894.] MYOLOGY OP RODENTS. 277 occiput, from the ligamentum nuchas, and from the anterior three or four dorsal spines and supraspinous ligaments ; the insertion is into the whole length of the vertebral border of the scapula, the occipital fibres also going to the fascia over the inner part of the supraspinatus. Sciurus and Pteromys differ in having a slight separation between the occipital and cervical portions, but this is not seen in Xerus and Spermophilus. Serratus Magnus and Levator Anguli Scapulce.-These two muscles are in the same plane and usually have a continuous origin, so that it is difficult to define their line of demarcation. They rise from the transverse processes of several cervical vertebrae, and from the sides of 7 to 9 of tbe anterior ribs by fleshy digita-tions. The insertion is into the vertebral border of the scapula. In the following animals a separate slip rising from the atlas was found :-Myopotamus, Sphingurus, Lagostomus, Sciurus, Pteromys, and Arctomys. The exact number of vertebrae and ribs from which these muscles arise in various Rodents are as follows :- Dipus cegyptius 1-7 c. v. 1-8 ribs. Capromys pilorides 2-7 „ 1-9 „ „ melanurus1 .... 3-7 „ 1-6 ,, Aulacodus 2-7 „ 1-9 „ Myopotamus 1st & 3-7 „ 1-8 „ Octodon 5-7 ,, 1-8 „ Hystrix 4-7 „ 1-8 „ Sphingurus 1-7 „ 1-7 „ Chinchilla 2-7 „ 1-9 „ Lagostomus 1-7 „ 1-8 Dasyprocta cristata 2-7 ,, 1-8 Ccelogenys 1-7 „ 1-8 Cavia cobaya 1-7 ,, 1-9 ,, Ceredon 2-7 „ 1-9 ,, Sciurus 1st & 3-7 „ 1-8 „ Pteromys 1-7 ,, 1-7 ,, Xerus 4-7 „ . 1-8 „ Arctomys marmotta .. 1st & 3-7 „ 1-9 „ Castor canadensis 2-7 ,, 1-7 „ 5) >? 5> Serratus Posticus.-This muscle varies very much in different genera and apparently in different individuals. Aulacodus seems to show most satisfactorily its full development. In this animal the anterior part of the muscle rises from the ligamentum nuchae and spines of the anterior dorsal vertebrae to be inserted into the ribs from about the 4th to the 12th, the direction of its fibres being backwards and outwards. The posterior part rises from the spines of the posterior dorsal and lumbar vertebrae by means of the lumbar £ascia, and runs forwards and outwards to the posterior 1 Dobson, P. Z. S. 1884, p. 234. PROC. ZOOL. Soc-1894, No. XIX. 19 |
