226 



MR. P. CHALMEUS MITCHELL ON SO-CALLED 



very degenerate, the cLaracteristic fusion witli the tibia towards 

 the proximal end being specially well marked. 



Supracoracoideal crest. — The supra'^'oracoideus muscle (pecto- 

 ralis secundus) is one which tends to become very highly 

 developed among pigeons. It is well known that its insertion 

 on a special ridge of the humerus is a peculiar feature of pigeon 

 osteology. This ridge is specially well developed among the 

 eutaxic forms, but it would be difficult to say more than that 

 this special development of pigeon anatomy was well marked in 

 them. On the other hand, there is a crest of origin for this 

 muscle to which I cannot find that attention has been directed. 

 In its fullest development it is a T-shaped crest, the stem of the 

 T carrying out the line of the coracoid across the carina of 

 the sternum at right angles to the long axis of that bony pro- 

 tuberance, and the cross-piece of the T lying parallel to the 

 anterior edge of the carina, the lower limb running along the 

 line on the carina which separates the insertion of the two 

 pectoral muscles. This crest is extremely well developed 

 in C, the ventral limb of the cross-piece extending nearly half- 

 way down the carina (fig. 5). In all the eutaxic forms it is 



Fig. 5. 



Starnosnas cyanocephala. — Carina of sternum, showing supracoracoideus crest. 



very well formed, while the extent of its development among 

 diastataxic forms varies. It is just visible in Goura and Caloenas ; 

 it is well marked, so far as the stem of the T is concerned, in 

 Columba and Turtiir, and in pigeons generally it is noticeable, 

 as in most Passeres. But in the eutaxic forms the stem is 

 always very strong and the lower limb of the cross-piece well 

 marked, 



Coraco-sternal articulation. — A primitive feature, familiar in 



