AVES. 



277 



These movements are freely allowed in most 

 birds from the nature of the articulation of 

 the tympanic bone; but in the Struthious birds 

 they are more restrained, from the connection 

 of the bone with the descending zygomatic 

 process of the temporal bone ; the extent of 

 this attachment is greatest in the Emeu, where 

 it almost produces a complete fixation of the 

 tympanic bone. 



The inferior maxillary bone (p, Jig. 125, v, 

 Jigs. 126, 128,) is originally composed of twelve 

 distinct pieces, each lateral moiety being made 

 up of six. The anterior symphyseal or dental 

 portion of each ramus first unites with its 

 fellow at the symphysis; the two portions 

 which form the condyle (v, Jig. 126) next an- 

 chylose; the angular (v, Jig. 126), supra- 

 angular and opercular, or splenial pieces are 

 consolidated at a later period. The anterior 

 extremities of the angular and supra-angular 

 pieces are wedged into corresponding grooves 

 of the symphyseal element ; and the opercular 

 portion is extended like a splint along the 

 inner side of the gomphosis, by which the 

 preceding portions are united. 



The traces of the original separation of these 

 bones long remain in the semi-aquatic and aqua- 

 tic birds (Grallatores and Natatores), which, 

 as the lowest of the class, manifest their affinity 

 in this respect to the cold-blooded Ovipara, 

 where this complex structure of the lower jaw 

 continues throughout life. 



As the lower jaw, thus constituted, forms 

 with the upper jaw the principal organ of pre- 

 hension in birds, it presents many variations 

 of form and magnitude, which immediately 

 relate to, and are consequently indicative of 

 their mode of life, food, &c. These general 

 modifications will be treated of in relation to 

 the digestive function, but some of the less 

 conspicuous characters of the lower jaw may be 

 more appropriately considered in this place. 



The rami are in general completely anchylosed 

 at the symphysis, the extent of the united por- 

 tions varying considerably in different birds, 

 but occupying in most cases only a small pro- 

 portion of the jaw. In the Pelicans the rami 

 are united by the mere extremities, appearing as 

 if bent upon each other at the symphysis, and 

 supporting the dilatable sac which fills up the 

 intermediate space, like the hoop of the fisher- 

 man's landing-net. The symphysis is also of 

 very small extent in most other Palmipeds. 

 It is small in the Rasores and Cursores. In the 

 Storks and Cranes it extends along a third part 

 of the entire jaw. In the Flamingo, where the 

 anterior part of the jaw is bent down at an 

 obtuse angle, nearly half of the rami are 

 united. In the Skimmers (Rhyncops), Horn- 

 bills, and Toucans, two-thirds. In the Curlew 

 the two rami are in apposition for two-thirds 

 of their anterior extent, but are not anchy- 

 losed, and form, in this respect, the only 

 known exception to the rule. 



In diurnal Birds of Prey, in many of the 

 Parrot-tribe, in the Herons and Swans, each 

 ramus of the lower jaw forms an entire bony 

 plate. In the rest of the class a membranous 

 nnossified space is left at the place of union 



of the symphyseul with the angular, supra- 

 angular, and splenial elements. This defi- 

 ciency is of a longitudinal form, and is always 

 situated behind the middle of the ramus. 

 In the Bustards, Woodcocks, Curlews, Gulls, 

 Skimmers, Guillemots, Petrels, and Pen- 

 guins, there is a second foramen, of a rounder 

 figure, posterior to the preceding, and resulting 

 from a defective union of the angular, supra- 

 angular, and condyloid pieces. In the Casso- 

 wary this space is subdivided into several 

 small foramina. In the Emeu (Dromaius) and 

 Ostrich (Struthio) there is a single small fora- 

 men at the corresponding part. 



At the posterior part of each ramus the fol- 

 lowing processes are developed in various 

 degrees in different birds. The suprangular 

 piece ascends in a greater or less degree in 

 the form of a thin lamina with a gently rounded 

 outline, representing the coronoid process. 

 From the inner side of the condyloid piece 

 there extends a more marked process, which 

 may be called the internal angular ; and from 

 the posterior part of the ramus a third process 

 is continued, which may be termed the poster ior 

 angular process. 



The coronoid process is most developed in the 

 Parrots, Gulls, Herons, and Cross-bills (Loxia), 

 in some of which, as the Loxia coccothraustes, 

 cardinally and pulverulentus, the lower jaw 

 presents the following peculiarity. A large 

 sesamoid bone of a triangular form, but 

 rounded and transverse, with the base directed 

 outwards and the apex inwards, is situated 

 at the posterior and internal aspect of the 

 articular ligament of the lower jaw. It com- 

 pletes the maxillary articulation posteriorly, and 

 corresponds by its anterior articular surface to 

 the posterior part of the outer condyle. The ar- 

 ticular surface of the lower jaw of the Parrots 

 is a simple narrow longitudinal furrow, open at 

 the two extremities. That of the Toucans is 

 almost equally simple, but of a rounder figure. 

 In most other birds the articular surface is 

 divided into two distinct portions, of which 

 the internal is an oblique concavity, the exter- 

 nal also oblique, but terminating in a convex 

 eminence behind. 



In the Rasorial birds the coronoid process is 

 feebly developed, but the internal and angular 

 processes are of large size. The latter is very 

 remarkable in the great Cock of the woods, 

 ( Tetrao urogallus,) where it extends upwards 

 and backwards in a curved form for the extent 

 of an inch, affording attachment to the power- 

 ful muscles required to produce the wide ex- 

 pansion of the mandibles necessary to seize the 

 large fir-cones which constitute its food. In 

 the lamellirostral Palmipedes not only are the 

 internal, and the posterior angular processes of 

 large size, but there are also two eminences for 

 muscular attachment on the outer side of each 

 ramus anterior to the articular surface. In the 

 Gulls an oblique ridge is continued from a 

 single eminence similarly situated. 



The articular capsule of the lower jaw is 

 strengthened by ligamentous fibres arising 

 from the lower extremity of the tympanic 

 bone, and passing backwards to be inserted into 



