1908.] OF THE BAXRACHIAN GENUS HEMISUS. 905 



first place, that there is here not simply the matter of a mviscle 

 extending loosely over the proximal region of the thigh during 

 its relaxed condition. The edge of the rectus which lies upon the 

 thigh is bound down to the skin of the leg by a septum of con- 

 nective tissue (text-fig.177, d.) which forms the wall of a lymph-sac 

 belonging to the system of femoral lymph-sacs. When this septum 

 and the flap of muscle is cut through transversely by a pair of 

 scissors, the section is seen to be V-shaped, the edge of the V being, 

 of course, the line along which the wall of the lymph-space ah^eady 

 referred to is inscribed. The ventralmost flap of the V is natu- 

 rally the muscle exposed on a dissection from the ventral surface, 

 and is what has been described as the rectus abdominis. The more 

 dorsal flap is folded under this up to the very line (the mid- 

 ventral line of the body) where the muscles of the two sides of 

 the body meet, and is inserted on to the edge of the pubis. 

 Although here the fibres of the superficial flap of muscle are 

 accurately antero-posterior in direction, while those of the sub- 

 jacent flap are exactly at right angles to them — running, that is to 

 say, in a lateral direction — the directions of the fibres become 

 coincident at the apex of the V which the two flaps of muscle form. 

 It should now be mentioned that the deep-lying flap of muscle 

 of which the fibres are consistently lateral in direction throughout 

 is not a continuation of the obliquus internus. The membranous 

 sheet which represents the latter muscle in this region of the 

 body underlies and is free from the layers of muscle which have 

 just been described. The lower flap of the muscle of one side of 

 the body is quite distinct from that of the other, since they are 

 divided by the line of the pubis from each edge of which they 

 arise. The superficial flaps are, however, quite united in the 

 middle line, and posteriorly, at any rate, no linea alba is to 

 be seen. 



The siobmeutalis (text-figs. 176, 178, m., pp. 899, 906) has 

 a shape which is evidently influenced by the shape of the 

 jaw and is also a considerably larger muscle than in Rana. 

 The anterior extremity of the lower jaw, instead of forming a 

 uniform curve as in Eana, has a perfectly straight or square 

 region anteriorly, which is shown in the accompanying text-figure 

 (text-fig. 178). The breadth of the jaw here is fully 5 mm., and 

 the length of the submentalis is therefore only a little less and it 

 has not in so mai'ked a degree as in other Frogs a lenticular shape. 

 It has the form of ii. cylinder tapering to both extremities. Its 

 -fibres can be seen to run straight across from one side of the jaw 

 to the other in the middle region of the muscle. At both ends 

 they curve upwards and are inserted into the angle of each man- 

 dibular i^amus where the straight anterior portion of each, which 

 is at right angles to the longitudinal axis of the body, passes into 

 the side of each ramus. I have described in Rhinoderma darioini * 

 a pair of ti-iangular muscles lying behind the submentalis which 

 I compared to the genioglossus. It might perhaps — though at 

 * P. Z. S. 1908, p. 686, text-tig. 146 a. 



