STRUCTURE OF BIRDS. 21 



posed of several distinct bones, which, however, soon unite, so 

 that all traces of their sutures become obliterated. In the 

 skull properly so called, or cranium, there are two frontal, two 

 parietal, two temporal bones, with an occipital, a sphenoid, and 

 an ethmoid. The cavity formed by these bones is in some 

 measure divided into two portions, of which the anterior eon- 

 tains the cerebrum, while in the posterior are lodged the cere- 

 bellum, the Q-ptiQ lobes, and the medulla oblongata. The face 

 is composed of the nasal, intermaxillary, malar, lachrymal, 

 superior maxillary, and palatal bones, with the vomer, and the 

 lower maxillary bone. The upper jaw, composed of all the 

 bones mentioned except the last, is united at its base with the 

 frontal, the ethmoid, and the temporal bones, but in such a 

 manner as generally to allow a considerable degree of motion, 

 wdiich is not however effected by joints properly so called, but 

 by the elasticity of the parts. Viewed from beneath, it pre- 

 sents two outer or anterior, and two posterior, slender branches, 

 which are articulated behind to a bone of irregular, somewhat 

 square form, named the t}Tiipanic bone, or os quadratum, which 

 is itself articulated to the temporal bone, and forms the anterior 

 edge of the cavity of the ear, having the membrane of the tym- 

 panum attached to its posterior margin. This arrangement, 

 owing to the motion given to the t}Tnpanic bone, and the 

 elasticity of the parts at the junction of the frontal and nasal 

 bones, allows the upper mandible a degree of motion varying 

 in the different families. The lower jaw of an adult bird is 

 formed of a single bone, having the sides generally thin and 

 nearly vertical, and articulated to the tympanic bone. 



Fig. 1 represents 

 the skull of the Ra- 

 ven, Cortus Cor ax ^ 

 viewed laterally. The 

 occipital bone, «, ori- 

 ginally composed of 

 Fig. 1. Skull of Raven. f^^j. pieces, the an- 



terior or basilar; the posterior, spinous, or superior; and 

 the two lateral or condyloid. The temporal bone is com- 

 posed of the petrous portion, b, containing the ear ; the 



