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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![an interior from the zygomatic arch. 1 have verified this in Arctomys, and find (lie description applies lo all the Seiuromorplia. In the Hystricomorpha it is difficult to satisfactorily separate the upper and middle portions. In those animals, such as Dipus, Chinchilla, and Xenis, where t he posterior part of the skull is broad, the two temporals do not meet in the mid line above. Masseter.—For the purposes of description it is most convenient to divide this muscle into four parts—anterior and posterior super- ficial, and anterior and posterior deep. These parts do not always show a distinct line of demarcation. The anterior superficial part rises by tendon from the side of the maxilla, and is inserted into the lower border and internal surface of the mandible, extending up to the insertion of the internal pterygoid. The posterior superficial rises from the whole length of the zygomatic arch, and is inserted into the lower part of the external surface as well as the lower border of the mandible. The anterior deep part differs in the Hystricomorpha and the Seiuromorplia. In the former, among which the Dipodidse are- included, this portion rises from a large area on the side of the maxilla, and then passes backwards and downwards through the enlarged infraorbital foramen to be inserted by a narrow flat tendon into the alveolar margin of the mandible, external to the molar teeth. In the Seiuromorplia this part of the muscle rises from the top of a vertical groove in front of the anterior portion of the zygomatic arch, the muscle runs down in the groove with- out passing through the infraorbital foramen and is inserted as in the Hystricomorpha. The posterior deep part rises from the lower border and some of the internal surface of the zygoma, and is inserted into the greater part of the external surface of the ramus of the mandible. The arrangement used here is practically the same as that adopted by Meckel, the only difference being that he describes the whole superficial part under one name (juc/o maxillien), although he states that the anterior border has a very strong superficial tendon; this anterior tendinous portion I have found to be easily separable from the rest in the Hystricomorpha, while in the Seiuromorplia it is separated by a distinct interval. Buccinator— This muscle is always well developed in Rodents, but in most cases shows no special points of interest. It rises from the maxilla and mandible opposite the molar and premolar teeth, and running forwards blends with the orbicularis oris. In Spermnphilus it is produced into the long cheek-pouch which, when empty, lies folded back on the cheek, having a muscular slip passing from the end of the pouch to the region of the shoulder. Facial Muscles.—The orbicularis palpebrarum is not very strongly developed ; from the anterior margin of it a muscle rises bv a narrow origin, but spreads out to be iuserted into the upper lip blending with the orbicularis oris, it probablv represents the [3]](https://iiif.wellcomecollection.org/image/b2238635x_0007.jp2/full/800%2C/0/default.jpg)
