76 STRUCTURE AND CLASSIFICATION OF BIRDS 



this is to mass the fleshy and heavy parts of the muscle 

 about the centre of gravity of the body, a desideratum for a 

 flying animal. This peculiarity of the muscular system, is 

 especially well seen in the muscles of the leg. The muscular 

 system of birds is remarkably constant for the species, the 

 number of variations being apparently, comparatively speak- 

 ing, but slight. It is true that in but few cases has a large 

 number of individuals been . carefully dissected ; but of a 

 good many species, on the other hand, have three, four, or 

 even more individuals been dissected from the point of view 

 of the relations or presence of a particular-ffluscle or muscles. 

 The muscular system too is apt to be very constant for a 

 given genus or even a larger division. A glance at the 

 systematic part of this work will show how trifling are the 

 variations even between families in some cases. All these 

 facts lead to the inference that the muscular system in birds 

 is of very considerable value for classificatory purposes. 

 Gaerod, Forbes, and Purbhingbr are the three anatomists 

 who have laid greatest weight upon the muscular system as 

 an index of affinity. It is, thinks Professor Furbringbe, the 

 muscles of the anterior extremity which have the greatest 

 value of any part of the muscular system. The wing is an 

 organ which is used in much the same way by all birds 

 in which it is properly developed. On the other hand the 

 uses of the muscles of the leg are manifold ; we have hopping 

 birds, climbing birds, perching birds, swimming birds, &c. 

 &c. Nevertheless Gadow is inclined to think (with Gaerod) 

 that they are the most important. The existing knowledge 

 of the muscles of birds is mainly confined to the muscles of 

 the leg and of the fore limb, a knowledge which we owe 

 almost entirely to Garrod and Furbringbe, many other 

 anatomists having, of course, filled up many details. Less is 

 known about the muscles of the head, neck, trunk, and hyoid 

 region. 



It is curious, indeed, how very few birds have been 

 at all thoroughly dissected. Apart from the detailed account 

 of Apteryx by Sir Eichard Owen, and of less comprehensive 

 memoirs by Coubs on the diver, by Morrison Watson 



