166 GENEBAL OBNITHOLOGY. 



cipal relic, in birds, of a set of splint-'bones which lie about the edges of the orbits in many 

 Sauropsida. Another is the post-frontal or sphenotic, usually a process of the frontal, often a 

 separate ossification. In some birds, as various Baptores, there are one or more loose supra- 

 orbital plates of bone, serving to eke out the brim of the orbits ; thus forming the " orbitaJ 

 shields " so prominent in many hawks, and causing their eyebrows to project. Were such a 

 a chain of splint-bones complete (lacrymal, superorbitals, post-frontal, and squamosal, to 

 quadrate), it would form an arcade of bones over the orbit, like the actual zygomatic arch 

 (maxillary, jugal, qnadrato-jugal, to quadrate) which lies under the orbit ; and such a double 

 series is very perfectly illustrated in many of the Sawropsida below birds (Huxley). 



Other special ossifications have been described in some birds, but I am obliged to pass 

 them over. 1 have already far exceeded intended limits, and have yet to describe the mandib- 

 ular and hyoidean arches, and the zoological characters of the palate as a whole. 



The Mandible, or Lower Jaw Bone (figs. 62, 63, 70, 71) is a collection of bones devel- 

 oped in the first post-oral visceral arch. Each half of the compound bone (right and left) con- 

 sists normally of five bones, which become immovably anchylosed, but traces of the original 

 distinction of which commonly persist for an indefinite period, — in some birds throughout their 

 lives. In an embryo whose skuU has passed to the cartilaginous stage, a long slender rod of 

 cartilage appears in the first post-oral visceral arch ; this is Meckel's ca/rUlage, or the meckeUoM 

 rod (figs. 65, 66, 68, 70, mk), so named after a famous anatomist. Around this rod, which 

 subsequently disappears, the several bones of the mandible are developed. The anterior one of 

 these is the dentary (ci), forming the scaflbld of the horny part of the external under mandible. 

 It usually unites by anchylosis, sometimes only by suture, with its fellow of the opposite side. 

 This union in the middle line is the symphysis (Gr. <ruv, swn, with ; ^uo-is, phusis, growth). 

 The line of union is externally the gonys (see p. 103), the length and other characters of which 

 are determined by the mode of symphysis, as is the general shape of the tip of the lower mandi- 

 ble. The union generally makes an angular _A., but may be an obtuse fl ; the symphysis is 

 very short and imperfect, as in a pelican, for instance, or the opposite, as in a woodpecker and 

 a multitude of birds. Behind the dentary, each ramus of the jaw continues with pieces called 

 splenial, angular and surcmgular (sp, a, su); there is often a fenestra between them, by 

 imperfection of bony union, as shown in fig. 63, or 63, /, which also sufficiently indicates the 

 relations of these parts. The articulation of the jaw with the quadrate bone is furnished by a 

 fifth piece called articular {cur) from its function. As a whole the mandible is a pronged bone, 

 forking with a variable degree of divergence from its obtuse or acute point, sometimes quite 

 parallel-sided, as in a duck, oftener very open; such prongs may be straight, or variously 

 curved or bent either in the vertical or the horizontal plane ; are generally stout and stanch, 

 sometimes so slender as to be quite flexible. The articular pfirt, always expanded horizontally, 

 presents a smooth irregularly oupped superior surface for reception of the protuberances of the foot 

 of quadrate. In general, the concave articular surface is divided into an inner and outer cup sepa- 

 rated by a protuberance, corresponding to similar inequalities of the opposing surface of the 

 quadrate. Cupping of the mandibular articulation is characteristic of birds as compared with 

 mammals, in which latter the lower jaw has always a knobbed articular surface (condyle). In 

 many birds the angle of the jaw is prolonged back of the articulation as a posterior articular 

 process (fig. 63, h, 70, 71, pap'), which may be long, slender and up-curved, as is well shown in 

 a fowl, duck, or plover. Such birds are said to have the " angle of the mandible recurved ; " 

 the opposite condition is "angle truncated" (cut off). Usually also, an internal angular 

 process (figs. 70, 71, iap) is produced inward from the articular part of the jaw, as in the 

 fowl, duck. Between the dentary and articular parts, the ramus of the jaw is usually verti- 

 cally produced as a thin raised crest, which, when prominent, is called the coronoid process ; 

 it corresponds to the strong process so called in a mammal, and relates to the advantageous 



