THE PIGEON. 195 



60. The quadrate (gu\ a short, stout, irregular bone, 

 articulating by a double head with two facets in the dorsal 

 region of the tympanic cavity, the upper of the two facets 

 being furnished by the squamosal, the lower by the prootic : 

 from its articulation, the quadrate takes a direction down- 

 wards and forwards ; its inner border sends off a large 

 pointed ascending process directed upwards, inwards, 

 and forwards, while its distal end forms a transverse cylin- 

 droidal articular surface or condyle for the mandible. 



6r. The columella (Fig. 48), a small and delicate rod 

 cf bone, having its expanded inner end fixed in the fenestra 



s.st.. 



St .JtSP^^ ~~~^::: v: 3 '^'^-^ C. St. 



I. St. 



FIG. 48. Columba livia. The columella auris ( x 8). 

 The cartilaginous parts are dotted. 



e.st, extra-stapedial : i.st, infra-stapedial : s.st, supra-stapedial : st, 

 stapes. 



ovalis, a small aperture in the inner wall of the tympanic 

 cavity, while its cartilaginous outer end is fixed, in the entire 

 head, to the inner surface of the tympanic membrane (see 

 3 J 7> P- 250.) 



The columella consists of a slender bony rod, having at its inner end 

 an oval plate of bone, the stapes (st), and at- its outer end a tri-radiate 

 cartilage : the central division of the latter, forming the direct con- 

 tinuation of the stapedial rod, is the extra-stapedisl ; the second 

 division, situated dorsally, is the supra-stapedial (s.st) ; the third, 

 central in position, the infra-stapedial (i.st) ; the supra- is connected 

 with the extra-stapedial by an oblique bar of cartilage. 



62. The pterygoids (Fig. 47, //), short, stout, paired 

 bones on the base of the skull, each articulating behind 



o 2 



