THE EXTERNAL STRUCTURE OF BIRDS. 165 
va 
9 
ig. 146. 
5 

PreryL&® oF Dorsau anv VentRAL Surraces or THE SwiFt, Cypselus apus. 
(After Nitzsch.) 
Fig. 146. Ventral aspect. Fig. 147. Dorsal aspect. 
1. Dorsal or spinal pteryla. 2. Humeral pteryla. 3. Femoral pteryla. 
4. Cranial pteryla. 5. Alar pteryla. 6. Caudal pteryla, 7. Crural 
pteryla. 8. Ventral pteryla. 
