ANATOMY OF BIRDS 



243 



mining as they do the form of the upper mandible, their shapes are 

 as various as the bills themselves of birds ; but their generalised 

 characters can be easily given. Each premaxillary, right and left, 

 forms its half the bill ; the two are always completely fused 

 together in front, commonly preserving traces at least of their 

 original distinction behind. They are commonly called one bone, t)ie 

 premaxillary. Each is a triradiate or 3-i)ronged bone ; one upper 

 prong, the most distinct, called the nasal or frontal ])rocess, forms 

 with its fellow the culmen (Fig. 26, h) of the bill. These pro- 

 cesses, side by side, run clear up to the frontal bone in birds, 

 driving the nasal bones apart from each other. Such a median 

 fronto-premaxillary suture, with lateral frontonasal and nasopre- 

 maxillary sutures, is highly characteristic of birds, — an arrangement 

 probably exceptionless. Two other horizontal i^rongs on each side, 

 extensively distinct from the frontal process in most birds, but 

 less separate from each other, run horizontally along the side and 

 roof of the mouth for a variable distance. These horizontal prongs 

 are an external or dentary process (Fig. ^0,ppx), forming the tomium 

 (Fig. 26) of the bill, and reaching back to join the dentary part of 

 the maxillary; and an internal or palatal process (Fig. SO, pjxc), run- 

 ning along the commencement of the bony palate. With this latter 

 the anterior ends of the palatal bones unite, — either on the side to- 

 ward the mid-line of the beak, or between the palatal and dentary 

 processes, as in a woodpecker (Fig. 80). Great laminar expansions 

 inward of these palatal parts of the premaxillaries roof the hard 

 part of the mouth anteriorly, though there is usually a vacancy 

 betAveen the })remaxillary hard palate and that formed farther back 

 by the maxillopalatines and palatines. The posterior extremities 

 at least of the frontal processes of the premaxillaries are commonly 

 distinguishable from each other as well as from the frontal and 

 nasal bones — in fact, these fronto-naso-premaxillary sutures are 

 among the most persistent of all. The divergence of the frontal 

 from the palatal and dentary processes bounds the external nostril 

 in part, the circumscription of that orifice being completed by the 

 prongs of the nasal bones. The superficies of the premaxillary 

 bone, like that of the dentary piece of the lower jaw-bone, is com- 

 monly sculptured with the impressions of the vessels and nerves 

 which ramify beneath the horny integument ; and in birds with 

 very sensitive bills, as a snipe or duck, the end is perforated sieve- 

 like with little holes, into which the skin shrinks in drjang, produc- 

 ing the familiar pitted appearance (Fig. 63, at c). 



The Nasal Bones (Figs. 62, 71, n) might have been described 

 next after the frontals, as they continue forward the general roofing 

 of the skull ; but are conveniently considered in the present con- 

 nection, being in birds rather "facial" than "cranial." They are of 



