Class ,5. Aves. 



439 



The skull consists of almost the same bones as that of Reptiles (but pre- 

 and post-frontals, transverse bone, and columella are always wanting). The 

 vomer is an unpaired bone of varied form, sometimes compressed, sometimes 

 fau'ly broad, etc., lying below the hinder portion of the nasal septum, and 

 connected behind with the palatine, in the movement of which it takes part. The 

 lachrymal lies at the anterior edge of the orbit, and in many Birds remains 

 distinct thi-oughout Ufe. The lower jaw consists of several bones on each side, 

 of which the anterior (dentary), in all living Birds, fuses very early with its fellow 

 of the other side ; in extinct toothed forms [Odontornithes), on the contrary, they 

 remained separate. 



Fiff. 364. 



Fig. 365. 



Fig. 364. SkuU of two days old Chick, a aliephenoid, d. 

 dentary, / frontal, j jugal, I lachrymal, mx maxilla, n nasal, na outer 

 cartilaginous wall of the nasal cavity, o orbital plate, ol ex-, os supra- 

 occipital, p parietal, jpa palatine, pm premaxilla, pt pterygoid, q 

 quadrate, qj quadratojugal, sq squamosal, st ear bones. The parts 

 which are still cartilaginous are dotted, the membranous portions 

 shaded. — After K. Parker. 



Fig. 365. Hyoid of the Fowl, h hyoid (anterior horn), hr first 

 branchial arch (posterior horn). — After K. Parker. 



The hyoid consists of an unpaired^ partially ossified median rod 

 (copula), to which is added (not invariably) a pair of very 

 short anterior cornua, and a pair of long posterior 

 cornua, the first branchial arch. The median rod is usually 

 divided into two or three pieces, lying one behind the other. 

 The cornua are not closely connected with the skull; the posterior 

 pair bend round the back part of the skull, but in the Woodpeckers, 

 where the tongue is specially protrusible, they curve up more 

 anteriorly, even as far forward as the base of the beak. 



The shoulder girdle (Fig. 366) consists of the usual elements. 

 Both scapula and c o r a c o i d are completely ossified ; the former 

 is a flat, narrow, sabre-shaped bone, which is generally connected 

 with the coracoid at an acute or right angle; the coracoid is 

 as a rule, rather long and narrow as compared with that of the 

 Reptiles, but yet very strong; its lower broad end articulates with 

 the anterior edge of the sternum. In Eatitse, and in some Odont- 

 ornithes, which were also incapable of flight, the two bones lie more 



