SKULL — BIRDS 



177 



reptiles which otherwise is absent. Except when the supraorbitals 

 are present, the frontals form most of the supraorbital border. 



The nasals, arising on the hinder part of the nasal capsules, 

 bound the nares more or less completely, the shape of those openings 

 having some systematic importance. Usually the nasals fuse with 

 frontals, ethmoid, maxillae and premaxillae, but when the beak is 

 mobile (p. 170) a joint comes between frontals and nasals. 



The premaxillae, forming the greater part of the beak, arise from 

 centres on the prenasal cartilage and are always fused in the middle 

 line, and laterally to the maxillae. Each has palatine, lateral and 

 ascending processes, the latter reaching the frontal. The maxillae, 



Fig. 191. — Schema of bones in bird skull (Newton, '93-96); cartilage bones dotted, 

 cartilage lined obliquely, a, articulare; an, angulare; as, alisphenoid; b^, ist branchial; 

 bo, basioccipital; bs, basisphenoid; c, columella; d, dentale; e, ethmoid; eo, e.xoccipital; 

 /, frontal; h, hyoid; I, lacrimal; tn, ma.xilla; n, nasal; os, orbitosphenoid; p, parietal; 

 pi, palatine; pm, premaxilla; ps, rostrum (Ppresphenoid) ; pt, pterygoid; q, quadrate; 

 qj, quadratojugal; so, supraoccipital; 5^, splenial; sq, squamosal; v, vomer; 2, zygomatic. 



pyramidal in shape, vary greatly in size, being the most conspicuous 

 bones, the premaxillae excepted, in herons, while they are very small 

 in fowl. They he ventral to the posterior part of the nasal capsule 

 with which their palatine processes are fused. Each articulates 

 behind with the (usually present) zygomatic which forms the anterior 

 part of the zygomatic arch. It and the following quadratojugal 

 are long and slender, the latter articulating with the quadrate, the 

 arch playing a part in transfer of motion from the quadrate to the 

 beak. 



There is usually a prefrontal at the anterior border of the orbit, 

 its varying relations being used by systematists. It is usually per- 



