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Show 1896.] MYOLOGY OF RODENTS. 183 Adductor Indicis.-The adductor indicis was present in all the animals examined except Bathyergus, Georgchus, and Heteromys; in the latter it was replaced by an adductor hallucis, which in the other specimens was wanting, although Windle describes it in Hydromys1. Prof. Cunningham has pointed out (Journ. of Anat. vol. xiii. p. 11) that the foot of Bathyergus is peculiar in the total absence of plantar adducting and dorsal abducting muscles. This statement, which also applies to Georychus, I a m able to corroborate. The muscle which I have described as abductor hallucis corresponds to Prof. Cunningham's inner head of the flexor brevis hallucis, though in his specimen the origin of the muscle was not so far back as in mine. In no Rodent were any distinct dorsal interosseous muscles found. Interossei.-There are two interossei, or flexores breves, to each toe inserted into the sesamoid bones beneath the metacarpophalangeal articulation. Myological Chcwacteristics of the various Families of Myomorpha. The animals of which the muscles have been described furnish examples of four families of the Myomorpha, namely the Myoxidce, Muriclce, Spalaciclce, and Geomyidce. Unfortunately the first and last of these are each represented in m y dissections by only one individual, and for this reason any generalizations must be made very tentatively. Still it seems worth while making an admittedly imperfect contribution in the hope that it may be added to and corrected whenever fresh material is available. In the first place, taking Myoxus dryas as a type of the Myoxidce, one notices that:- 1. The biceps cubiti is only inserted into the radius. 2. The coraco-brachialis is only represented by the second part. 3. The palmaris longus is absent. 4. The flexor sublimis digitorum is inserted into the fifth digit as well as into the second, third, and fourth. 5. The extensor minimi digiti is only inserted into the fifth digit. 6. The trapezius has the second and third parts fused. 7. The trachelo-mastoid is absent. 8. The rectus abdominis does not decussate at its origin with its fellow of the opposite side. 9. The gracilis is single. 10. The soleus rises from the middle of the fibula instead of from the head of that bone. 11. The tendon of the tibialis posticus lies in the same groove as the flexor fibularis instead of in one of its own. In the Geomyidce, of which Heteromys longicaudatus is the only representative dissected, the following points are of interest:- 1. The digastric approaches the hystricomorphine type. 2. The semitendinosus has only the caudal head present. 1 P. Z. S. 1887, p. 58. |
