On the myology of the sciuromorphine and hystricomorphine rodents / by F.G. Parsons.

  • Parsons, Frederick Gymer, 1863-1943.
Date:
1894
Catalogue details

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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    levator labii superioris of human anatomy. The anterior belly of the occipito-frontalis may be made out as a thin layer of muscle running upwards from the upper border of the orbicularis palpe- brarum ; it is quite distinct in Hystrian. The other facial muscles, including those of the lower lip, are indistinguishable from the facial panniculus. (See fig. 10.) Pterygoid Muscles.—The external pterygoid is small and rises from the very feebly marked external pterygoid plate or rather ridge; it is inserted into the inner side of the neck of the condyle and the bone just below. The internal pterygoid rises from the outer side of the internal pterygoid plate or pterygoid bone, and has the usual human insertion. In Sphingurus the internal muscle consists of two distinct layers ; with this exception the above description applies to all the animals examined. Digastric.— The digastric is attached posteriorly to the front of the paroccipital process, while anteriorly it is inserted into the inner surface of the mandible. There are two absolutely distinct types of the muscle. In the Hystricomorpha the two bellies are not separated by a real tendon as in Man, although there is a slight constriction of the muscle, and a thin layer of tendon on the surface especially below ; the attachment to the hyoid bone is very feeble, and the two anterior bellies are separated from one another by a distinct interval in which the mylo-hyoid is exposed. The anterior attachment is a considerable distance from the symphysis. In the Chinchillkke the attachment to the hyoid bone is well marked. In the Hystricidae the above description applies in Hystncc, but in Sphingurus the posterior belly ends in a tendon which is firmly inserted into the hyoid bone; from the anterior or upper side of this tendon the anterior belly runs to its attachment on the mandible. The sciuromorphine type of digastric is well described by Kunstler1 in the Marmot. The anterior and posterior bellies are separated by a distinct tendon which is firmly attached to the hyoid bone. From the inner surfaces of the tendons of the two sides fibrous bands run inwards to meet one another, forming a tendinous arch with its convexity in front. From the front of this arch the two anterior bellies spring ; they are in contact in the middle line nearly as far as the symphysis, where they separate a little to expose the transverse mandibular muscle. The tendinous arch gives attachment to some of the fibres of the mylo-hyoid as well as the anterior bellies of the digastric. This arrangement is common to all the Sciuromorpha (Sciurus, Pteromys, Xerus, Spermophilus, Arctomys, Castor) as well as the Dipodithe (Dipus cegyptius, D. hirtipes, Alectaga indica). Transverse Mandibular Muscle.—This muscle is accurately described by Kunstler in the Marmot; it was present in all the Kodents with a movable symphysis menti examined. I have not 1 Annales des Sciences nafurollcs, s6r. 7, t. iv. n. 150 [4]