The value of myology as an aid in the classification of animals / by F.G. Parsons.

  • Parsons, Frederick Gymer, 1863-1943.
Date:
1895
Catalogue details

Licence: Public Domain Mark

Credit: The value of myology as an aid in the classification of animals / 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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    quite possible to place a specimen in its proper family by referring to the combinations of muscles which are characteristic of that family, l'or instance, the absence of a scalenus anticus in a hystricomorphine rodent vv.ould at once make me suspect that it was a porcupine ; if it wanted a peroneus quarti I should suspect it of being a tree- porcupine ; and if in addition it had two heads to the biceps cubiti, a well-developed omo-hyoid, and a levator clavicular rising from the atlas, I should feel pretty certain that it was one. The question which I should expect to be asked, and which, indeed, has been asked, is “ What light does myology throw on the position of the Dipodidae ? ” Dobson1 says that the only argument for placing them among the Myoinorpha is the fact that the tibia and fibula are fused, while in favour of including them in the Hystrico- morpha are the united flexors in the sole, the masseter passing through the infraorbital foramen, the external appearance of the ears and muzzle, the armed condition of the penis, and the arrangement of the teeth. With regard to the fused tendons, I have been able to point out two examples of myomorphine rodents in which these are present. The large size of the infraorbital foramen is a question of degree, since in most myomorphine rodents a small piece of the masseter passes through this opening, and it is only in sciuromorphine and lagomorphine rodents that the infraorbital foramen transmits nothing but the nerve. With regard to the classificatory value of teeth, Mivart, in his work on the THuroidea,2 has given grounds for not placing much confidence in them, and, for my own part, I cannot help thinking that, unless used with considerable caution, they are apt to mislead. I can add another claim to those which Dobson has given for regarding the jerboas as hystricomorphine, and that is that they have only one head to the biceps cubiti, while every myo- morphine rodent that I have looked at possesses two. On the other hand, in addition to the fusion of the leg-bones, which is never seen in the Hystricomorpha, the two halves of the lower jaw move upon one another and are provided with a transverse mandibular muscle ; the digastric is arranged on the sciuromorphine type described by Kunstler,3 a type which is never found in the Hystricomorpha, but often in the Myomorpha; the scapulo-clavicularis, which 1 have already laid stress on as being a most constant muscle in the Hystri- comorpha, is absent; and the omo-hyoid is present as in all the Myomorpha, while it is often absent in the Hystricomorpha. On the whole, I certainly think that the myology of the jerboas points to their having myomorphine rather than hystricomorphine tendencies, though their many points of difference from both groups might entitle them to subordinal rank, as Dipodomorpha. With regard to the affinities that Dobson believes them to have with the Chinchillidae, a i Proc. Zool. Soc., 1882, p. 640. *Proc. Zool. Soc., 1882. 3 Ann. Set. Nat., ser. 7, t. iv., p. 150.