550 



MK. D. W. DEVANESEN ON THE 



posterior thick division, P.A. 4, inserted on to the upper surface 

 of the same plate. As regards the 2jetrohyoicleus-posterior (P.P.), 

 while a small part of it clings to the cartilaginous free end of a 

 posterior cornu, the bulk of the fibres pass above the latter and 

 are inserted to the pharynx, a few fibres reaching also to the 

 larynx, I could not find any trace of the omo-hyoid muscle, a 

 negative feature observed also in Breviceps and Tlemisiis. 



Of the muscles of the tongue, it may be noted that the relative 

 position of the two divisions of the genioglossus has undergone 

 an alteration. The one corresponding to the outer part in Rana 

 lies above the other corresponding to the median part of this 

 muscle. Further, the former has shifted its insertion from the 

 mucous membrane of the floor of the mouth to the body of the 

 tongue (text-fig. 16 E), 



Text-figaire 17. 



P.S.A. 



PS. A. 



View of certain muscles of the cliest. Ou tlie right side the portio-sternalis- 

 anterior' sa\&. \\\e portio-abdo'Minis h&ve been removed. S.H., stej'no-radialis ; 

 P.S., fortio-scapularis or the vestigial deUoideus; P.S.A., 'portio-sternalis- 

 anterior; P.S.A'.,, cut end of the same on the right; C.H., coraco-Jmmeralis ; 

 P.A',, outer division of the portio-abdominis ; P.A.", an inner division of the 

 same muscle ; X., xiphisternum. 



It seems to me that the specialisation described above of the 

 muscles of the hyoid and of the floor of the mouth is in some 

 way connected with a more efficient method of obtaining food. 



The muscles of the chest as a whole, with the exception 

 of the 2y07^tio-ste7'nalis-anterior and the portio-abdominis, exhibit 

 a feeble development (text-figs. 13 & 17). This, in my opinion, 

 is mainly due to the disappearance of the pre-coracoid, the 

 omosternum, and the episternum. For instance, the sterno- 

 radialis, which arises in Rana from the three elements of the 

 pectoral girdle mentioned, has its origin shifted to the inner 

 ventral border of the coracoid, which is less extensive ; conse- 

 quently this muscle is vestigial*. Again, the delioideus exhibits 

 a degeneration in the absence of one of its two divisions, 



* In this connection it may be mentioned that this muscle is absent in. 

 Breviceps (1). 



