On the myology of the sciuromorphine and hystricomorphine rodents / by F.G. Parsons.
- Frederick Gymer Parsons
- Date:
- 1894
Licence: Public Domain Mark
Credit: On the myology of the sciuromorphine and hystricomorphine rodents / by F.G. Parsons. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
12/48 page 260
![In Octodon, a and ft rise respectively from the anterior and posterior halves of the sternum and are not so closely united. 1 n the Hystricidte a forms a separate band which runs obliquely across the rest of the muscle to be inserted quite at the lower half of the humerus, some fibres passing to the fascia of the fore- arm. y and 8 are inserted with ft ; so that this family is remarkable for having the insertion of the pectoral almost entirely into the humerus (Hystrix, Sphingurus, Erethizon dorsatus1). The ChinchillidcB resemble the Octodontidae in having a and ft fused, c in the Chinchilla is inserted into the outer part of the clavicle, but in the Viseacha it is inserted into the coracoid process and first rib external to the origin of the subclavius. In the Dasyproctidae a is a distinct oblique slip as in the Hystricidse. y is inserted into the upper extremity of the humerus. S in Dasyprocta goes to the outer part of the clavicle blending with the sternoscapular. In Coelogenys this part was not seen. This description differs from that of Mivart and Murie 2 in classing part of their peetoralis as deltoid. I find that the portion in question is supplied by the circumflex nerve and not by the anterior thoracic; as the circumflex also supplies the deltoid it is probable that the slip belongs to that muscle instead of to the peetoralis. (See Deltoid.) Jn the Caviida) there are no special fibres rising from the costal cartilages (Cavia cobay a, Ceredon rupestris). In the Sciuromorpha a has the usual origin and is inserted about the middle of the humerus, ft rises from the whole of the sternum and runs almost horizontally to the whole of the pectoral ridge, y joins t) at its insertion. S rises from the 2nd, 3rd, and 4th cartilages in Sciurus and Pteromys; from 2nd, 3rd, 4th, 5th, and Oth in Arctomys and Spermophilus. The insertion is into the shoulder-capsule and the coracoid process. Sterno-scapularis.—This muscle consists of two parts which display a good deal of variety in different members of the group. The internal part or subclavius rises from the first rib at its junction with the sternum and is inserted into the posterior surface of the outer third of the clavicle. The outer part or scapulo-clavicularis, when it is present, rises from the clavicle close to the insertion of the subclavius, with which it is usually more or less continuous, and is inserted into the spine and vertebral border of the scapula, covering the supraspinatus as a broad thin sheet. In the Dipodidse the scapulo-clavicularis is absent but the sub- clavius is well marked (D. cegyptius, D. hirtipes, Alectaga indica). In the Octodontidae the two parts of the muscle communicate very slightly if at all in Octodon, Myopotamus, Capromys pilorides and C. mclanurus3, but in Aulacodus many fibres are continuous. In the Hystricida) the two parts are continuous in Hystrix, hut quite separate in Sphingurus. 1 P. Z. S. 1882, p. 281. 2 P. Z.8. 18(iB. p. 383. :i Dobson, P. Z. 8. 1881, p. 234. [10]](https://iiif.wellcomecollection.org/image/b2238635x_0014.jp2/full/800%2C/0/default.jpg)
