Nov, 1895. MUSCLES AND CLASSIFICATION. 337 



rises from the fibula, and the " flexor longus' digitorum," which comes 

 from the tibia. As these names are quite misleading when apphed to 

 the lower animals, Dobson has very wisely suggested the terms 

 "flexor fibularis " and "flexor tibialis," respectively. In the whole of 

 the sub-order of the Hystricomorpha, or porcupine-like rodents, these 

 two tendons join in the sole ; in the squirrel group, or Sciuromorpha, 

 they do not join, but the flexor tibialis is inserted separately into one 

 of the tarsal bones. In a specimen of the flying squirrel [Ptevomys 

 oral), I found the flexor tibialis dividing, one half joining the flexor 

 fibularis, while the other had the insertion usual in Sciuromorpha. 

 The mouse-like rodents (Myomorpha) are placed by the systematists 

 nearer to the squirrels than to the porcupines ; consequently one is 

 not surprised that the long tendons are arranged as in the former 

 animals. I have, however, been somewhat interested to find two 

 exceptions, the bamboo rat {Rhizomys badius) and the pocket mouse 

 [Heferoviys longicaiidatus). One of the most curious things is that the 

 jerboas have the tendons united, and in this respect approach the 

 Hystricomorpha. Dobson lays the greatest stress on the value of 

 these tendons as an indication of natural position among the rodents ; 

 but I am inclined to think that they should be used carefully and 

 only in conjunction with other muscles. It is largely owing to the 

 arrangement of these tendons that Dobson claims a place for the 

 Dipodidae among the Hystricom.orpha, but I have just been able to 

 show that among the Myopiorpha a similar arrangement exists in 

 Rhizomys and Heteromys. To this question of the position of the 

 Dipodidae I return later. 



Another noteworthy muscle is the " sterno-scapularis." This 

 consists of two parts : one running from the first rib, at its junction 

 with the sternum, to the clavicle, and corresponding entirely to the 

 human subclavius ; the other reaching from the clavicle over the 

 supraspinatus muscle to the spine of the scapula. These two parts 

 are often continuous beneath the clavicle, and are supplied by the 

 same nerve. The first part, the " subclavius," is always present ; 

 the second part, the " scapulo-clavicularis," is never found in the 

 Sciuromorpha, but was present in every specimen of the Hystrico- 

 morpha examined, with the exception of the jerboas, whose position 

 is still unsettled. The hare-like rodents (Lagomorpha), as one would 

 expect, resemble the Hystricomorpha in the presence of the muscle, 

 while the Myomorpha approach the Sciuromorpha in wanting it. 

 Among this latter group, however, are two exceptions in which it is 

 present ; namely, the African mole-rats, Bathyergus and Georyclms. 

 The former of these has already been suspected of affinities with the 

 Hystricomorpha on account of the structure of its mandible, and it is 

 interesting to notice how the muscle seconds the testimony of the 

 bone. The action of this muscle must be to lessen the angle between 

 the clavicle and scapula, and so to make the glenoid cavity face more 

 downwards. This action is, doubtless, most useful in digging, and it 



