24 ME. F. E. BEBDARD ON THE [Jan. 14, 



This latter is, as I take it, the ohliquus internus. In the middle 

 line it can be seen to be covered by the very thin stei-nal poi-tion 

 of the rectus abdominis. Here its fibres run ol)liquely forwai'd 

 from the median line, fairly parallel indeed in direction with the 

 fibres of the adjacent and covering pectoralis abdominis. From 

 the inscriptio tendinea the fibres of the obliquus internus run 

 dii-ectly forward parallel to the long axis of the body ; more 

 laterally they run postero-anterioi-ly but obliquely towards the 

 median ventral line of the abdomen. Passing round the abdomen 

 the direction of the fibres is gradually changed, until anteriorly 

 just behind the shoulder-girdle the fibres of the obliquus internus 

 run exactly at right angles to the long axis of the animal's body. 

 The obliquus internus, therefore, of Brevicejjs is very different 

 from that of Rana, Avhere the fibres run obliquely postero-anteriorly 

 with a main dorso-ventral direction and with but a slight fanning 

 out from the back towards the venti'al sui-face. In £reviceps the 

 fanning is much more marked and is in the opposite direction, 

 i. e. the fibres converge towards a point upon the ventral surface 

 on each side of the body. This point, or rather area,, is formed 

 by the origin of a very strongly marked muscle, flat and of con- 

 siderable diameter, from the septum between itself and the 

 obliquus internus and rvmning forward parallel with the sternum 

 to be attached to the hyoid. I term this muscle the hyo-ahdom- 

 inalis, and I regard it as being, like the omo-abdominalis, a 

 portion of the obliquus externus. Against this view, however, is 

 the fact that it is, in the greater part, covered by the omo-abdo- 

 minalis. I would further remark that this muscle apparently 

 has its homologue among the Pelobatidfe *, where, however, it 

 is not quite so impoi-tant as in Breviceps and has a diffei-ent in- 

 sertion. I am disposed to i-egard this peculiar arrangement of the 

 obliquus internus and its relation to a large hyo-abdominalis and 

 the large size of the omo-abdominalis, as being connected with 

 the ant-eating habits of Brevicejis. The arrangement of the 

 muscles in question is such as to produce a powerful pull upon 

 the hyoid apparatus and tongue. The very slender sternal portion 

 of the rectus is to be associated with the I'udimentary and reduced 

 state of the cartilaginous stern vnii. The large omo-abdominalis is 

 possibly associated with the bvii'rowing habits of the Frog. It 

 would assist in producing a strong pull upon the shoulder- 

 girdle. 



The abdominal musculature therefore of this Frog agrees with 

 that of other Anura in the possession of only two layers of muscle. 

 But the exact homology between the variously metamorphosed 

 regions in this and other Anura is clearly difficult to settle. The 

 obliquus internus, as I have termed the inner sheet of muscle, 

 seems to be comparable not only with the obliquus internus of 

 Rana but to that muscle ^jZhs certain parts of the rectus 

 abdominis. For the anteriorly directed fibres of the muscle in 



* Beddard, " On Megaloplirys nasuta," P. Z. S. 1907, p. 340 ; id., " On Pelobatidse," 

 ihid. p. 894. 



