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.
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![gurus, and presumably in Erethizon dorsatus and epixanthus, as it is not mentioned by Mivart1 or TV indie2. In the Chinchillidse it rises from the upper part of the fibula, the p. quinti being absent (Chinchilla, Layostomus). In the Dasyproctidae it rises from the whole outer surface of the fibula in Dasyprocta, in which there is no p. quinti; in Cceloyenys it only rises from the lower third of the bone. In the Caviidse it resembles the Chinchillidse in Ceredon and Cavia cobay a. Beddard mentions that it is present in Dolichotis. It is always present in the Sciuromorpha, having the usual attachments. In Sdurus, Pteromys, Xerus, and Spermophilus it rises from the lower quarter of the fibula and runs to the fourth digit. In Arctomys marmotta it sent an additional slip to the third toe. In Castor it was joined by a small muscular slip from the calca- neum, probably part of the extensor brevis digitorum. It will be noticed that the only auimals in which this muscle was wanting were the Tree-Porcupines. Peroneus Quinti Diyiti.—The p. quinti when it is present rises from the outer surface of the fibula above the last muscle, and is inserted into the extensor longus tendon on the dorsum of the fifth toe. It is present in the Octodontidse (Myopotamus, Capro- mys, Octodon, Aulacodus), in the ITystricidae (Hystrix, Sphinyurus, Erethizon), in Cceloyenys, and in all the Sciuromorpha examined. It is absent in Pipits cegyptius, in the Chinchillidse (Chinchilla, Layostomus), in the Caviidae (Cavia cobay a, Ceredon, Dolichotis), and in Dasyprocta. The presence or absence of the p. quinti seems to depend entirely on the degree of development of the fifth toe. It is not nearly as persistent a muscle as the extensor proprius hallucis, which is so often found when no hallux exists; it seems indeed to precede the disappearance of its toe, because in Chinchilla the muscle is wanting, although there is a small fifth toe. Gastrocnemius.—The gastrocnemius rises by two heads from the upper and back part of the two condyles, fabellse often being present. The two heads unite with the soleus to form the tendo Achillis. The fibres of this tendon are twisted so that those that are derived from the inner head of the gastrocnemius become superficial and eventually external. In Castor canadensis the two heads remain separate as far as their insertion. The presence or absence of the fabellse does not seem to depend on the affinities of the animal, as they are large in Aulacodus on both sides, while in Myopotamus only the outer one is present. In Dasyprocta they are both present, in Cceloyenys both absent. In the Sciuromorpha, however, they were found in every case except that of Castor canadensis (Sdurus, Pteromys, Xerus, Sper- mophilus, Arctomys, Castor). Soleus.—The soleus rises in all cases from the posterior aspect 1 P.Z.S. 1882, p. 271. 2 Journ. Anat. vol. xxii. p. 126. [41]](https://iiif.wellcomecollection.org/image/b2238635x_0045.jp2/full/800%2C/0/default.jpg)
