262 



THE PIGEON 



represented by the rostnun). The basi-sphenoid (basi-temporal) and rostrum 

 form the base of the cranium. 



Behind the basi-temporal is the basi-occipital, which bears the single condyle 

 for the articulation of the skull with the atlas vertebra. The basi-occipital, the 

 two ex-occipitals, and the supra-occipital surround the foramen magnum 

 (through which the spinal cord passes), and together form the back of the 

 cranium. 



The roof of the cranium is formed by the paired parietals and frontals ; and 

 at its sides are the tympanic cavities, with the squamosals above and the basi- 

 temporal below. Each squamosal has a projecting zygomatic process which 

 meets the descending post-orbital process of the frontal. 



Frontal 



Maxilla 



Parietal 



Premaxilla 



Maxilla- 

 Rostrum, 



Frontal Maxillo-palatine 



Interorljital septum / Po^f-orbital process process 



_' /' .' o{ Frontal 



Palatine— - 



Quadrate 



Pterygoid 

 Quadrate. 



E''°"'P'«»'Basitempora'l 



-Tympanic cavity 



., Eustachian tube Exoccipital- 



, Ouadrate Basioccipita^ 



\ Occipital condyle 



Articular Supraoccipital 



C. B. 



Fig. 91.— The Skull of the Pigeon {Columha). A. Dorsal view ; B. Ventral view ; C. Lateral view. 



The facial region of the skull comprises the small nasals, the long triradiate 

 premaxillse (which together form the greater part of the upper beak), and the 

 bones of the upper jaw and the bony palate or roof of the mouth. The nasals 

 are forked bones ; the two processes of each meet the ascending and outer pro- 

 cesses of the premaxilla; and enclose the external nares. Each side of the upper 

 jaw consists of premaxilla, small maxilla, and quadrato-jugal, with a jugal over- 

 lapping parts of the latter two bones. Note that as the jugal has no ascending 

 process meeting the zygomatic (of the squamosal), the orbit is therefore con- 

 fluent with the temporal fossa behind. The roof of the mouth is formed by 

 the palatines, connected in front with the inner parts of the maxillae (maxillo- 

 palatine processes) and premaxillae and behind with the rostrum of the basi- 

 sphenoid and the rod-like pterygoids, two obliquely-directed bones which 

 articulate behind with the quadrate. A^'hen the mouth is opened and the upper 



