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Show 184 MR. F. G. PARSONS ON T H E [Jan. 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. 6. 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 incision which had been made for evisceration before the specimen came into m y hands. The family of the Muriclce is represented by accounts of the dissection of nine animals, and I a m only able to discover one muscular 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 wdth the muscle of the opposite side. When one considers what a large and heterogeneous 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 m y 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 more nearly allied to one another than is the case in the Muridae: in other words, that the classification of the Hystricomorpha is more successful than that of the Myomorpha. While speaking of the Muridae, it is worth noticing that Cricetus and Cricetomys are the only two of the Myomorpha examined which possess the first part of the coraco-bracbialis or rotator humeri muscle. In many particulars, however, they differ from one another. In the family of the Spalacidce there are records of three animals, Bathyergus, Georychus, 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 Georychus 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 fabellae 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 Georychus and Bathyergus on the other:- 1. In Rhizomys the digastric has a well-marked central tendon, in Bathyergus and Georychus there is only an intersection. 2. In R. the cleido-mastoid is overlapped by the first part of the trapezius ; in B. and G. it is not. 3. In B. and G. the scalenus anticus is present. In R. it is absent, as it is in all other Myomorpha except Gerbillus. |
