1908.] ANATOMY OF A FROG. 15' 



which does not arise from its edge. When this first section of 

 the petrohyoideus posterior is raised, it is seen to overlie the 

 posterior portion of the petrohyoideus anterior, which latter 

 therefore is a more extensive muscle than is usual among the 

 Batrachia Salientia. 



The petrohyoideus posterior secundus is attached in the present 

 species as is the petrohyoideus posterior tertius of some other 

 Frogs. It is inserted, in fact, on to the expanded lower extremity 

 of the thyrohyal bone. Whether some fibres escape to be con- 

 nected with the laryngeal apparatus I do not know. 



The 2)etrohi/oideus posterior tertius is quite different in its. 

 relations from the corresponding muscle in other Frogs whose^ 

 anatomy is known. In order to see the muscle the secundus has. 

 to be raised. When this is done, the muscle now under discussion 

 is seen as a somewhat slender muscle running parallel with thfr 

 other parts of the petrohyoideus posterior. But it has no 

 relations whatever to the thyrohyal bone. This in itself is a 

 point of likeness to the Pelobatidse. But the resemblance ceases, 

 with this. For in £revice2)s the muscle avoiding altogether the 

 end of the thyrohyal ends in close juxtaposition to the oesophageal 

 muscle on the walls of the commencement of the lung (see text- 

 fig. 7, B). Its action on contraction would appear from its position 

 to be like that of the oesophageal muscle and would dilate th& 

 pulmonary cavity, 



§ Superficial Muscles of the Ventral Surface. 



The general appearance of these various muscles, after the skin 

 has been removed, is very different from the corresponding view^ 

 of the musculature of Rana. I shall proceed to describe these 

 several muscles, commencing with the rectus abdominis and 

 passing forward to the throat. All the muscles now in question 

 are shown in the accompanying figure (text-fig. 3). As is well 

 known, the thighs of this frog are included within the area of the 

 body, the portion of the leg from the knee onwards alone pro- 

 jecting beyond the contour of the trunk. But when the skin 

 was reflected and turned back, it was to be observed that the 

 area lying between the anterior border of the thigh and the 

 posterior border of the abdomen is not merely covered by skin. 

 For closely adherent to the skin in this region, and indeed 

 inserted upon it, is a layer of muscle (to be considered in greater 

 detail later, p. 26) attached on the other side to the leg which 

 bridges over the gap. The conditions are not, therefore, very 

 widely different from those which characterise Xenopus * and 

 Fi2xcf, where muscles attached to the leg spread into the 

 abdominal region and thus help to destroy the demarcation 

 between thigh and abdomen. 



The rectics abdominis muscle appears to me to have in pro- 



* Beddard, " On the Diaphragm &c. of Xenopus," P. Z. S. 1895, p. 844, tig. 3. 

 f Id. " On . . . the Anatomy of Pipa," ibid. p. 838, fig. 4, 



