166 GENERAL ORNITHOLOGY. 



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-froutal or sphenotic, usually a process of the frontal, often a 

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

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

 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 foiTn an arcade of bones over the orbit, like the actual zygomatic arcli 

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

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



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

 them over. I 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 cartilage, or the meckelian 

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

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

 these is the dentary (d) , forming the scafi"old 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. (rvv, sun, with ; i^va-ig, plmsis, 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 genei'ally makes an angular ^, but may be an obtuse Q ; 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 

 S2)lenial, angular and surangular (sp, a, si(); there is often a fenestra between them, by 

 imperfection of bony union, as shown in fig. 62, or 63, /, which also sufl5ciently indicates the 

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

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

 foi'king with a variable degree of divergence from its obtuse or acute point, sometimes quite 

 parallel-sided, as in a duck, ofteuer 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 part, always expanded horizontally, 

 presents a smooth irregularly cupped 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 ^wsierior articular 

 process (fig. 63, li, 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 recun-ed ; " 

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

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



