496 MANUAL OF ZOOLOGY SECT. XII 



straight, sometimes wavy, sometimes zig-zagged, serrations 

 of the edges of the two bones interlocking ; in some cases 

 the edges of the bones are bevelled off, and the bevelled 

 edges overlap, forming what is termed a squamous suture. 



Another conspicuous difference between the skull of the 

 rabbit and that of the pigeon is in the mode of connection 

 of the lower jaw, which in the former articulates directly with 

 the skull, the quadrate, through which the union is effected 

 in the pigeon, being apparently absent. Certain large 

 apertures which are distinguishable are readily identified with 

 the large openings in the skull of the pigeon. In the pos- 

 terior wall of the skull is a large rounded opening, the 

 foramen magnum, flanked with a pair of smooth rounded 

 elevations or condyles for articulation with the first vertebra, 

 these obviously corresponding to the single condyle situated 

 in the middle below the foramen in the pigeon. A large 

 opening situated at the end of the snout and looking forwards 

 obviously takes the place of the external nares of the pigeon ; 

 and a large opening in the roof of the mouth leading forward 

 to the external nasal opening, plainly represents, though 

 much wider and situated further back, the internal or poste- 

 rior nares of the pigeon ; while the rounded tubular opening 

 situated at the side of the posterior part of the skull, some 

 distance behind the orbit, is evidently the same as the 

 auditory aperture of the pigeon. 



Surrounding the large opening of the foramen magnum 

 are the bones of the occipital region of the skull, the supra-ex- 

 and basi-occipitals. The first of these ( s. oc ) is a large plate 

 of bone above the foramen magnum. The ex-occipitals lie 

 at the sides of the opening and each bears the greater part 

 of the somewhat oval prominence or condyle with which the 

 corresponding surface of the atlas or first vertebra articulates. 

 The bast-occipital is a median plate of bone, almost horizontal 



