ON THE PERONEAL MUSCLES IN BIRDS. 1039 



60. The Peroneal Muscles in Birds. By P. Chalmers 

 MiTCHELL,M.A.,D.Sc.,LL.D.,F.R.S.,F.Z.S., Secretary 

 to the Society. 



[Received October 28, 1913 : Read November 25, 1913.] 

 (Text-figures 179-190.) 



Index. 

 Steuctuee. Page 



MrOLOGT. 



Peroneal Muscles in Chauna 1040 



S.ystematic Description of Peroneal Muscles in Aves 1043 



JStiologt. 



Distribution of Varieties of Peroneal Muscles in the 



System 1068 



Adaptation and Descent 1070 



Systematic, 



Fandion 1050, 1072 



Caprimulgi 1062, 1072 



In the dissection of an example of Balceniceps rex, which formed 

 the basis of a recent contribution to the Society's Proceedings 

 [supra, pp. 644-703), I was interested to notice that one of the 

 very few characters in muscular anatomy which the Shoe-bill 

 shared with Herons, to the exclusion of Storks, was the presence 

 of the leg muscle l^nown as the Peroneus brevis or profundus. On 

 looking up the literature relating to the peroneal muscles in birds, 

 I found that even Dr. Gadow's careful description of these muscles 

 (Gadow in Bronn's ' Thier-Reich,' Aves, pp. 180-182) was based 

 on a relatively small number of individuals and types, and that 

 his work, together Avith the insignificant contributions of earlier 

 and later writers, supplied only a vague and dubious picture of 

 the anatomical facts in Aves. I wished to make a survey of 

 these muscles as nearly as possible complete. Accordingly I have 

 dissected them in the birds that have died in the Society's Collec- 

 tion for some months, have made use of the rich spirit material 

 stored in the Prosectorium (most of it dating from the time of 

 Garrod and Forbes), and have been alloAved to examine some 

 specimens in the stores of the British Museum (Natural History) 

 and of the Museum of the Royal College of Surgeons, and 

 Dr. Gadow has also obliged me with material from Cambridge. 

 My observations therefoi-e relate to several hundred birds, dis- 

 tributed, as Avill be seen later, fairly well over the whole Avian 

 system. Theoretically, no doubt, it is necessary to work out the 

 complete anatomical structure of an animal if one would under- 

 stand any portion of it, but in practice this is impossible, and in 

 my opinion the examination of a single structure or even portion 

 of a structure through the whole series by a single observer can- 

 not fail to be interesting and instructive. The method, moreover, 



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