i896.] MYOLOGY OF BODEIfTS. 185 



4. la B, and 0. the sterno-scapularis is present. In B, it is 

 absent. 



5. In B. and G. the teres major is inserted in front of the latis- 

 simus dorsi, in R. behind it. 



6. The coraco-brachialis is absent in G., small in my specimen 

 of B., absent in Milne-Edwards's specimen. In B. the second and 

 third parts are well marlsed. 



7. In B. and G. the extensor communis digitorum sends no slip 

 to the fifth digit. In B. 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 B. 



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 B. 



10. The rectus abdominis does not decussate with its fellow of 

 the opposite side in B. or (?., though it does so in B. 



11. The gracilis is a single muscle in B. It is distinctly double 

 in B. and G. 



12. The flexor tibialis joins the flexor fibularis in the sole of B. 

 The two tendons are separate in B. and Q-. 



13. The adductor indicis pedis is absent in G. and B., present 

 in B. 



It will thus be seen that, though there are six more or less un- 

 important points of resemblance between Bhizomys on the one 

 hand and Baihyergus and Georychun 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 true 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 

 Baihyergus 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 

 I'elated, 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 Bhizomys, 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 tliis characteristic is present in Bhizomys, it is worth 



