184 MB. F. G. PABSONS ON THB [Jani 14, 



3. The gracilis is a single muscle. 



4. The flexor tibialis joins the flexor fibularis in the sole. 



5. There are only three lumbricales in the foot. 



G, There is an adductor hallucis instead of an adductor indicis 

 in the foot. 



Whether the rectus abdominis decussated with its fellow of the 

 opposite side, could not be determined owing to the large incisipn 

 which had been made for evisceration before the specimen came 

 into my hands. 



The family of the Muridce is represented by accounts of the 

 dissection of nine animals, and I am only able to discover one mus- 

 cular peculiarity which is common to them all and at the same 

 time distinguishes them from other families, — this is the fact that 

 the rectus abdominis always decussates with the muscle of the 

 opposite side. When one considers what a large and hetero- 

 geneous family this is, and that many of the genera included in it 

 are only placed there provisionally, one is not surprised to find 

 that their musculature is not nearly so consistent as it was found 

 to be in the different families of the Hystricomorpha. 



To my mind the fact that the latter show definite muscular 

 characteristics which are not found in the former, indicates that the 

 hystricomorphine families consist of animals which are morenearlj' 

 allied to one another than is the case in the Muridre : in other 

 words, that the classification of the Hystricomorpha is more success- 

 ful than that of the Myomorpha. 



While speaking of the Muridas, it is worth noticing that Gricetus 

 and Cncetomys are the only two of the Myomorpha examined which 

 possess the first part of the coraco-brachialis or rotator humeri 

 muscle. In many particulars, however, they differ from one 

 another. 



In the family of the Spalacidai there are records of three animals, 

 Dathyergus, Oeoryclms, and Rhizomys. The following points of 

 resemblance were noticed in this group : — 



1. The temporals are large and meet in the middle line of the 

 head. 



2. The stylo-hyoid and stylo-glossus are closely blended in 

 Rhizomys, while in Oeorychiis the stylo-hyoid is absent or completely 

 fused with the other muscle. 



3. The pronator quadratus is very feeble. 



4. The reflected head of the rectus is ill-marked. 



5. The gastrocnemius has no fabellffl in its tendons of origin. 



6. There are three lumbricales in the foot. 



The following are points of difference between Rhizomys on the 

 one hand and Oeorychus and Bathyergus on the other; — 



1. In Rhizomys the digastric has a well-marked central tendon, 

 in Bathyergus and Oeorychus there is only an intersection. 



2. In B. the cleido-mastoid is overlapped by the first part of the 

 trapezius ; in B. and O. it is not. 



b. InJ5. and O. the scalenus anticus is present. In R. it is 

 absent, as it is in all other Myomorpha except Oerlillus. 



