SEC. IV ANATOMY OF BIRDS 245 



twisted, crooked, hooked, etc. It is singularly elongated and dis- 

 torted in the ostrich. In the duck tribe, in which the lacrymo- 

 frontal region of the skull is greatly elongated, the lacrymal has 

 coextensive attachment to the frontal bone, and is broadly laminar, 

 with a downward process ; in some ducks bounding at least a fourth 

 of the orbital brim, and almost completing the circle by extending 

 toward the very protrusive postfrontal process, as in Fig. 63, u. In 

 some parrots, the rim of the orbit is completed below, and even 

 sends a bony bar to bridge over the temporal fossa behind the 

 postfrontal. In some birds, the lacrymal is quite free, and even 

 in more than one free piece. The os uncinatum, or os lacrymo-pala- 

 tinum, would appear to be a palatine bone distinct from the lacrymal ; 

 it has been observed in the Musophagidce and many other picarian 

 birds, in Tachypetes, and certain Procellariidce. The lacrymal bone 

 seems to be the principal relic, in birds, of a set of splint-bones 

 which lie about the edges of the orbits in many Sauropsida. Another 

 is the postfrontal or sphenotic, usually a process of the frontal, 

 often a separate ossification. In some birds, as various Eaptares, 

 there are one or more loose supraorbital 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 pro- 

 ject. Were such a chain of splint-bones complete (lacrymal, 

 superorbitals, postfrontal, and squamosal, to quadrate), it would 

 form an arcade of bones, over the orbit, like the actual zygomatic 

 arch (maxillary, jugal, quadratojugal, to quadrate) which lies under 

 the orbit ; and such a double series is very perfectly illustrated in 

 many of the Sauropsida below birds. 



Other special ossifications have been described in some birds, 

 but I am obliged to pass them over. I have already far exceeded 

 intended limits, and have yet to describe the mandibular 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 developed in the first postoral visceral arch. 

 Each half of the compound bone (right and left) consists normally 

 of five bones, which become immovably ankylosed, but traces of the 

 original distinction of which commonly persist for an indefinite 

 period, — in some birds throughout their lives. In an embryo whose 

 skull has passed to the cartilaginous stage, a long slender rod of 

 cartilage appears in the first postoral visceral arch ; this is Meckel's 

 cartilage, or the MecMian 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 (d), forming the scaffold of the 

 horny part of the external under mandible. It usually unites by 



