"quijSttocubitalisjVi" in the wing op birds. 217 



directions. Erom this point of view, it might be said that even 

 were the eutaxic condition primitive it would not be surprising 

 to find that birds primitive in that respect were much specialized 

 in other directions. I am not yet prepared to meet this argument 

 fully in its application to pigeons; I can only say that I find 

 that where the lines of progressive change are clear, there appears 

 to me to be a high average of association among the changes. 

 Taking only the changes characteristic in a group, individuals with 

 flne of the changes well marked have a high average of the other 

 changes. Groups are, in fact, characterized by a tendency to par- 

 ticular variations in particular structures ; these variations are 

 individual and in a state of flux in the more primitive species, but 

 tend to become fixed as specific or generic characters in more 

 advanced types. 



Muscular Anatomy. 



M. rhomloideus superjicialis. — In the majority of Oolumhidce 

 according to Fiirbringer (4), and I am able to corroborate him, 

 the origin, of this muscle is fleshy. In A, a, B, C, and E it has 

 become tendinous, while in E part of the anterior end of the 

 muscle is a degenerate fibrous sheet. In the vast majority of 

 birds this muscle has passed into what is certainly the secondary 

 condition of being tendinous in origin. The Columbse are peculiar 

 in that most of them present the more primitive condition, but 

 in five out of the seven eutaxic forms this primitive condition 

 has been lost. 



W. supracoracoideus. — The great development of this muscle 

 is one of the special features of the anatomy of the Columbse. 

 In its highest development, it extends to the extreme tip of the 

 sternum and invades the keel to a considerable extent. A special 

 feature, which will be noticed with the osteology, is the tendency 

 to formation of a strong smooth ridge of insertion which carries 

 the line of the coracoid across the anterior edge of the keel. In 

 all the seven eutaxic pigeons the muscle and its ridges has 

 reached the extreme development found in the group. Asso- 

 ■ciated with this extreme development is a m.arkedly bipinnate 

 arrangement of the muscle-fibres on their central tendon; the 

 extent to which this occurs varies among pigeons, but is strongly 

 marked in all the eutaxial forms, 



M. coracohracliialis externus. — This muscle from the coracoid 

 to the planum bicipitalis of the humerus is a large muscle in 

 Eatites, but in Carinates is on the wane,' entirely disappearing 

 in some of the Passeres. In the Columbse generally it is very 



