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Show 182 MR. F. G. PARSONS ON T H E [Jan. 14, Plantaris.-This has the typical rodent arrangement, the only point of interest being the extent to which the muscular fibres of the flexor brevis digitorum are developed in the sole. In Gerbillus three little slips of muscle are alone seen in the intervals between the four tendens where they first separate. In Microtus the flexor brevis has no muscular fibres at all, while in Myoxus and Myodes there are very few. All the other animals examined had well-developed muscular bellies to the flexor brevis. Popliteus.-The popliteus always rises from the external condyle, and is inserted into the upper part of the internal border of the tibia. Flexor Longus Hallucis (Flexor Fibularis).-This is always a large muscle, rising from both the tibia and fibula and being inserted into the distal phalanges of ah the toes. Flexor Longus Digitorum (Flexor Tibialis).-Dobsonl states that this muscle in the Myomorpha is always separate from the flexor fibularis tendon in the sole. I have, however, met with two remarkable exceptions to this generalization, viz. Rhizomys and Heteromys. In both of these animals the tendons unite in the sole exactly as they do in the Hystricomorpha. I should mention that this arrangement was present in both the right and left feet. In Georychus and Bathyergus the muscle is better developed than in most of the Myomorpha, and ends in a bone beneath the base of the first metatarsal which I am inclined to regard as a rudiment of a praehallux. In all the other animals examined the muscle ends chiefly in the fascia of the foot. Tibialis Posticus.-This is always a small muscle and rises from the upper part of the posterior surface of the tibia below the attachment of the popliteus, and also very often from the back of the head of the fibula. As a rule it has a groove of its o w n behind the internal malleolus, but in Myoxus it shares the groove of the flexor fibularis. It is inserted into the under surface of the navicular, though in Mus rattus it goes chiefly to the plantar fascia. Muscles of the Foot. Lumbricales.-InGeorychus, Bathyergus, Rhizomys, and Heteromys only three lumbricales are present. All the other animals dissected have four. Accessorius.-This muscle is very ill-developed in the Myomorpha. The only animal in which I found it really well marked was in Bathyergus, although traces of it could be made out in Mus rattus. Abductor Hallucis.-This is usually present and rises from the navicular in Cricetomys, Rhizomys, Mus barbarus, and M. rattus. In Gerbillus, Cricetus, Microtus, Myoxus, Heteromys, and Georychus it came from the internal cuneiform. In Bathyergus it was Veil-marked and rose from the sustenaculum tali' of the calcaneum, its proximal part forming the calcaneo-scaphoid hgament. Journ. Anat, xvii. p. 142. |
