1908.] ANATOMY OF A FROG. 17 



The 2i^otorcdis muscle comes next in order and consists of the 

 usual three parts. The portio sterncdis anterior is very much 

 larger than the portio sterncdis posterior , and is at its origin in 

 the middle line nearly three times the diameter of the latter. 

 It is incompletely divided into two portions. There is no gap 

 between the two parts of the portio sternalis, nor between the 

 posterior of these and the portio cd>dom.incdis ; nevertheless the 

 several muscles are not in any way confused at their origins ; 

 they are perfectly distinct. The portio abdominalis is large and 

 important. It allows no trace to be seen of any scapular portion 

 of the obliquus externus such as is figured in Ecker's work upon 

 the Frog. It arises raainly from the surface of the rectus 

 abdominis in front of the single tendinous inscription of the latter. 

 There is also an origin not represented in Rana (or represented 

 indeed by the posterior part of the portio sternalis of that 

 Amphibian) from the expanded cartilaginous sternum. The 

 fibres of the two sides of the body here meet in the middle line of 

 the sternum. This region of the portio abdominalis is not, how- 

 ever, separated in any way from the rest of the muscle ; its fibres 

 lie side by side with those of the rest of the muscle and there is 

 no gap anywhere. Indeed, oia both sides of the body the sternal 

 fibres of the portio abdominalis actually overlap the hinder edge 

 of the portio sternalis posterior, that part of the latter muscle in 

 fact which arises from the iliomboidal cartilaginous sternum ; 

 for the latter muscle arises more from the edge of the sternum, 

 while the fibres of the portio abdominalis arise from the ventral 

 surface of the same cartilage. There being no omosternum in 

 Brevicejjs, there is no superficially visible equivalent of the 

 sternoradialis of liana. The only thoracic muscle visible in 

 front of the pectoralis is the clavicular head of the deltoid, which 

 is shown in the figure referred to (text-fig. 3, D). 



The throat-muscles visible on the supei-ficial view are again 

 different from those seen in Rana without any further dissection 

 than the removal of the skin. As in Rana, a large sheet of 

 muscle occupies the throat which obviously consists, as in that 

 Frog, of the suhmaxillaris and sid)hyoideus muscles. The tAvo 

 halves of each of these are separated along the median line by a 

 very narrow tendinous raphe. But whereas in Rana by far the 

 greater part of this sheet belongs to the suhmaxillaris, only a 

 slender slip posteriorly being referable to ,the subhyoideus, the 

 precise reverse is the case with Brevicej^s. In fact in the Frog 

 which forms the subject of the present memoir, the diameter 

 (antero-posterior) of the suhmaxillaris is 2-5 mm., and of the 

 subhyoideus is 5'5 mm., the measurements being taken near to 

 the middle line. This is accounted for of course by the reduced 

 lower jaw of B7-evicep>s ; but not entirely so, since fibres of the 

 muscle, which, did they continue in a straight course, would reach 

 the ramus of the lower jaw, bend posteriorly to form part of the 

 mass of the subhyoideus. It should be stated in explanation of 

 the above, that medianly there is no differentiation of the two 



Proc. Zool. Soc— 1908, No. II. 2 



