1896. j MYOLOGY OF RODENTS, 185 
4, In B. and G. the sterno-scapularis is present. In R. it is 
absent. 
5. In B. and G. the teres major is inserted in front of the latis- 
simus dorsi, in #. behind it. 
6. The coraco-brachialis is absent in G., small in my specimen 
of B., absent in Milne-Edwards’s specimen. In R, the second and 
third parts are well marked. 
7. In B. and G. the extensor communis digitorum sends no slip 
to the fifth digit. In 2. a slip to this digit is present. 
8. There is no sesamoid bone in the tendon of the supinator 
brevis in B. and G. There is one in R, 
9. The pair of interosseous muscles which should be inserted 
into the two sesamoid bones of the fifth digit of the hand are 
absent in B. and G. They are present in R. 
10. The rectus abdominis does not decussate with its fellow of 
the opposite side in B. or G., though it does so in R. 
11. The gracilis is a single muscle in R. It is distinctly double 
in B. and G. 
12. The flexor tibialis joins the flexor fibularis in the sole of R. 
The two tendons are separate in B. and G. 
13. The adductor indicis pedis is absent in G. and B., present 
in R. 
It will thus be seen that, though there are six more or less un- 
important points of resemblance between Jhizomys on the one 
hand and Bathyergus and Georychus on the other, there are 13 
points of difference, some of which, such as nos. 3, 4, 10, 12, and 
13, I regard as of great importance. 
The study of these marked muscular differences in animals 
whose habits are so much alike, and whose external appearances 
are so similar, seems to point to one of two conclusions. Either 
the external appearances are acquired by the animals living under 
similar conditions while the muscles tell the irue tale of their 
different ancestry, or else the differences in the muscles are of no 
value for classificatory purposes. 
Against the latter conclusion the evidence of the myology of 
Bathyergus and Georychus tells strongly; these animals are so 
alike in their habits, in their osteology, and in their visceral anatomy, 
that no one doubts that they are closely related; they are also 
alike in their myology with one or two trifling exceptions. This, 
however, is only one instance of the close resemblance of the mus- 
culature in animals which are for other reasons regarded as akin; 
and I cannot help thinking that when several important differences 
occur in the muscles of two animals which otherwise seem closely 
related, the muscles are trustworthy guides, because, taken as a 
whole, they are-less likely to adapt themselves quickly to changed 
conditions than are other structures. 
With regard to the position of Rhizomys, the junction of the two 
long flexors in the sole has been regarded by Dobson as character- 
istic of the Hystricomorpha, though I have found it in other 
animals, As this characteristic is present in Rhizomys, it is worth 
