1896. ] MYOLOGY OF RODENTS. 173 
In no case could I satisfy myself of the existences of an adductor 
or opponens pollicis. 
Muscles of the Little Finger.—These are not so easily made out 
as in the other Rodents. The abductor is present, but is not 
double. The flexor brevis is represented by the ulnar slip of the 
interosseus muscle to the little finger, when there happens to be a 
muscle in that position. I have never been able to find an 
opponens, although Windle describes it in Hydlromys. 
Lnterosset.—In all the animals examined, except Georychus and 
Bathyergus, there were eight interossei, the inuer of which formed 
the flexor brevis minimi digiti. In these two animals there were 
no interossei attached to the fifth finger, although the two 
sesamoid bones supposed to be developed in them were present. 
Practically the same arrangement was found in the Beaver. In 
Cricetomys, Microtus, and possibly in Cricetus, there was an 
adductor minimi digiti, which recalls the figure already published ' 
of the same muscle in Celogenys. In Rhizomys and Gerbillus 
there is an adductor indicis. These two muscles are situated on 
a plane superficial to that of the interossei, and I have not come 
across any Myomorphine animal which possesses both of them, 
although they frequently co-exist in the Hystricomorpha. 
Muscles of the Trunk. 
Panniculus Carnosus.—In the majority of the Myomorpha the 
panniculus corresponds to the rodent type already described. 
The sterno-facialis is always present, but seldom large. In 
Georychus and Bathyergus the panniculus, especially the anterior 
part, is very well developed; in the former the platysma is 
very strong and rises from the angle of the mouth and from the 
median raphe running back from the symphysis menti, it runs 
backward and upward to be lost over the region of the shoulders, 
though some of the more posterior fibres are attached to the 
metacromial process. When this is removed, the whole length 
of the sterno-facialis and epitrochleo-facialis comes into view, 
the former rising from the posterior half of the sternum, the 
latter from the internal condyle of the humerus; they both run 
forward to be inserted into the fascia on the surface of the 
masseter. In Bathyergus the sterno-facialis has undergone greater 
development, and is continuous posteriorly with the panniculus 
of the abdomen; this I have figured, and have pointed out? that it 
is a possible foreshadowing of the human sternalis muscle. The 
posterior part of the panniculus in Bathyergus is also well marked, 
and gets an attachment to the external tuberosity of the tibia and 
to the ramus of the ischium. In Heteromys among the Geomyide, 
the pouch causes a good deal of modification in the facial 
panniculus. The superficial part or platysma rises from the 
1 P. ZS. 1894, p. 273. 
? Journ. Anat. vol. xxix. p. xii. 
