166 GENERAL ORNITHOLOGY. 



cipiil relic, in birds, (if a set of splint-boucs whicli lie ubuut the edges of the orbits in nuiuy 

 Sauropsida. Another is the post-frontal cjr sphcnotie, usually a process of the frontal, often a 

 separate ossification. In some birds, as various Iluptores, 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 piromiuent in many hawks, and causing their eyebrows to project. Were such a 

 a chaiu of splint-bones complete (lacrynial, superorbitals, post-frontal, and squamosal, to 

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

 (ma.xillary, jugal, quadrato-jugal, to (puidrafe) \vhi<-h lies under the orbit ; and such a double 

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



(.)ther special ossifications have been descrilied in scjme birds, but 1 am obliged to pass 

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

 ular and hyoideau arclies, and the zoological characters of the palate as a whole. 



The Mandible, or Lower Jaw Bone (figs. ()2, (ili, 70, 71) is a ccdlcction of bones devel- 

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

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

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

 lives. In an eml)ryo whose skull 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. (i5, 66, 68, 70, mlc), so nanu'd after a famous anatomist. Around this rod, which 

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

 these is the deritary (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 <.ipposite side. 

 This um(.in in the middle line is the ftiimpliysia (Gr. (Tvv, x-an, with ; (j)va-is, phusis, growth). 

 The line of union is e.\tern.ally the gom/s (see p. 10^5), tlu> length and other characters of which 

 arc determined by the mude of symphysis, as is the general shape of the ti]> of the lower mandi- 

 ble. The uni(jn generally makes an angular J^, but may be an obtuse [\; the symphysis is 

 very slmrt and imperfect, as in a pelican, for instaiu'e, 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 snrangular (up, a, sii); there is often a fenestra bet^'cen them, by 

 imperfection of bony union, as sliowu in fig. 02, 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 (ar) from its function. As a whole the mandible is a pironged bone, 

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

 parallel-sided, as in a duels, oft.ener very open; such prongs may be straight, or variously 

 curved or bent either in the vertical or the horizontal ]>lane ; are generally stout and stanch, 

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

 presents a smooth irri'gularly cupped superior surface for recejition of tlie jirotuberances of the foot 

 (jf quadrate. In general, the concave articular surfaci' is divided into an imier and outer cup sepa- 

 rated by a protuberance, corresponding to similai- inecpuilities of the cqiposing surface of the 

 quadrate. Cupping of the mandibular articulation is (diarai-teristic of birds as compiared with 

 manunals, in which lattei' the lower jaw has always a knobbed articular surface (condyle). In 

 many birds the angh; of the jaw is pi-olonged bad; of tlie articulation as a posterior articular 

 process (fig. 68, h, 70, 71, pap), which may be long, sleniler and up-curved, as is well shown in 

 a fowl, duck, or plover. Such Idrds are said to have the " angle of the mandible i-eciirved ; " 

 the ojiposite condition is "angle truncated" (cut off). Usually also, an ■iiiternal angular 

 process (figs. 70, 71, iap) is produced inward from the .-irticular p.art of the jaw, as in the 

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

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

 it corresponds to the strong proc(,'ss so called in a manunal, and relates to the advantageous 



