AND DEVELOPMENT OF THE BIRD'S SKULL. 151 



growing young of a species of Podiceps, Qolymbus, Alca, or JJria ; they all specialize 

 by passing just a stage or so beyond the simple Pluvialine pattern, but in different 

 degrees. The Petrels are close congeners of the Gulls; many of the smaller kinds 

 retain their basipterygoids. A large number of water-birds keep their " lateral occi- 

 pital fontanelles " open throughout life. (See, on the Pluvialine types, Huxley, Proc. 

 Zool. Soc. 1867, pp. 426-431.) 



DESCRIPTION OP THE PLATES. 



Plate XX. 



Fig. 1. Vertical section through head of embryo Fowl [Gallus domesticus) , about the beginning of the 



sixth day of incubation, x 7 diameters. 

 Fig. 2. The same, taken further back through the eyeballs and nasal sacs, x 7 diameters. 

 Fig. 3. The same, behind the nasal walls, x 7 diameters. 

 Fig. 4. Part of same section, x 27 diameters. 



Fig. 5. A section further back, through the eyes, pituitary space, and lower jaw. x 7 diameters. 

 Fig. 6. Section through ear- sacs of the same embryo, x 7 diameters. 

 Fig. 7. A longitudinally vertical section of the hind face of an embryo of the House-Martin (Chelidon 



urbica). x 15 diameters. 

 Fig. 8. Inner view of auditory structure and mandible in a fledgling Carrion-Crow {Corvus corone). 



x 3 diameters. 

 Fig. 9. Os quadratum and stapes of adult Jackdaw {Corvus monedula). x 6 diameters. 

 Fig. 10. Stapes of Piping-Crow (Gymnorhina tibicen), inner view. X 10 diameters. 

 Fig. 11. The same, edge view, x 10 diameters. 



Fig. 12. Palatine view of skull of Starling (Sturnus vulgaris), x 4 diameters. 

 Fig. 13. A species of Cardinal (Cardinalis, ?sp.). x 5^ diameters. 



Plate XXL 



Fig. 1. Palate of embryo of Brown Linnet (Linota cannabina) of the sixth day of incubation. 



X 15 diameters. 

 Fig. 2. Part of same, x 150 diameters. 



Fig. 3. Part of embryo of same bird, seventh day of incubation, x 20 diameters. 

 Fig. 4. Vomer and part of palatines of a fledgling Sparrow (Passer domesticus), seen from above. 



x 4| diameters. 



