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Show 186 MR. F. G. PARSONS ON T H E [Jan. 14, while noticing that in no other respect does it approach the Hystricomorpha; consequently I think that the study of the muscles bears out the suggestion of Winge1 that Rhizomys is distinct from the Bathyerginae, and that it should be placed among the Muridae, which it resembles in the only common point which this family has-the decussation of the rectus. Winge1 also suggests that Bathyergus is closely allied to the Hystricidae. The following points in its myology show a divergence from the myomorphine and an approach to the hystricomorphine arrangement:- 1. The scalenus anticus is present and rises from the basi-occipital. 2. The scapulo-clavicularis is present, as in all Hystricomorpha, while in no myomorphine rodent was it found. These two points alone would not of course justify one in separating the Bathyerginae from the Myomorpha, but they show an approach to the hystricomorphine type which is suggestive. The Position of the Dipodidce. A review of the muscles of Rodents would be incomplete without considering whether they lend any assistance towards determining the vexed question of the position of the Jerboas. In m y former contribution I described their muscles with those of the Hystricomorpha. Now that the muscles of the Myomorpha have been worked out, a comparison can be made between them. In the following points the Dipodidae resemble the Hystricomorpha :- 1. The large size of the anterior deep part of the masseter passing through the infraorbital foramen. 2. The presence of a scalenus anticus rising from the basi-occipital. 3. The presence of only one head of the biceps cubiti. 4. The non-decussation of the rectus abdominis at its origin with the muscle of the opposite side. 5. The union of the tendons of the flexor tibialis and fibularis in the sole. The first point is only one of degree since the Myomorpha show a small piece of the masseter passing through the infraorbital foramen. The second has been found in Myoxus among the Myomorpha, as well as in Bathyergus and Georychus, whose position is not quite certain. The third point is certainly in favour of hystricomorphine tendencies, as I have not yet found any myomorphine rodent without two heads to the biceps cubiti. The fourth point, the decussation of the rectus, is not always found in the Myomorpha, while it sometimes occurs, as in the Octodontidae, among the Hystricomorpha. 1 E Museo Lundii, 1888, p. 109. |