186 ME. r. G. pahsons on the [Jan. 14, 



while noticing that in no other respect does it apjjroach . the 

 Hystricomorpha ; consequently I think that the study of the 

 muscles bears out the suggestion of Wings' that llhizomys is 

 distinct from the Batliyergince, 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. 



AVinge ' also suggests that Bathyergus is closely allied to the 

 Hystricidse. The following points in its myology show a diver- 

 gence from the myomorphine and an approach to the hystrico- 

 morphine arrangement : — 



1. The scalenus anticus is present and rises from the basi- 

 occipit.al. 



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 justifj" one in 

 separating the Bathyerginoa 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 Eodents would be incomplete without 

 considering whether they lend any assistance towards determining 

 the vexed question of the position of the Jerboas. In my former 

 contribution I described their muscles with those of the Hystri- 

 comorpha. Now that the muscles of the Myomorpha have been 

 worked out, a comparison can be made between them. 



In the following points the Dipodidce resemble the Hystrico- 

 morpha : — 



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 

 ji small piece of the masseter passing through the infraorbital 

 foramen. 



The second has been found in Myoxus among the Myomorpha, 

 as well as in Bathyenjus 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, tlie decussation of the rectus, is not always 

 found in the Myomorpha, while it sometimes occurs, as in the 

 Octodontidce, among tlie Hystricomorpha. 



> B Museo Lvndii, 1888, p. 109. 



