QUIJSTTOCUBirALISM IN THE WING Of UIEDS. 



219 



of the deltoides patagialis. In fip-. 2 B, I show it in a condition 

 which is usually primitive among pigeons, and which I found 

 as an individual abnormality in Oolumba livia. The whole slip 



Fig. 2. 



^PAT. 



Alar muscles of Columha livia. 

 PAT. Deltoides patagialis. Pec. Pectoralis propatagialis. B. Biceps pata- 

 gialis slip, an unusually primitive condition not common in Columha 

 livia, L. Longus tendon. A. Anconeus scapularis. D. Deltoides major. 

 B. Extensor metacarpi radialis. a. Fiirbringer's ' alpha ' slip. 



from its origin to insertion is muscular. In fig. 3 I the normal 

 pigeon-condition is shown. The origin from the biceps is 

 reduced to a rounded tendon or even a thin aponeurosis arising 

 partly from the wing-membrane. In fig. 3 II the most advanced 

 pigeon-development is represented. The muscle is now fully 

 specialized, and has a long tendon at each end with a consider- 

 able muscular belly. The insertion is now very low down on 

 the longus tendon, the tendon of the biceps slip running parallel 

 with that for a considerable distance. The muscle is in fact 

 losing its primitive function and becoming really more of an 

 accessory to the radial extensors. It appears to me to be a 

 probable suggestion that this extreme development may be 

 tending really to the final extinction of the muscle, and therefore 

 to a Passerine-like condition. My immediate point, however, is 



