THE PECTORAL ARCH IN BIRDS. 



247 



about that the upper jaw of such a bird as a Parrot rises, when, 

 in opening the mouth, the mandible is depressed. Each ramus 

 of the mandible consists primitively of six pieces, as in other 

 Sciuropsida^ but the dentary pieces of each side are, as in the 

 Chelonia, very early united, if indeed they are not ossified 

 from one centre. Verv often, a fontanelle remains between 

 the dentary and the other elements, as in Grocodilia ; and 

 the dentary long remains readily separable from the rest ; or, 

 as in the Goatsuckers, is united mth the others only by fibrous 

 tissue, so that it is movable. The angle of the mandible may 

 be truncated or produced backward into a long curved pro- 

 cess, as in Fowls (Fig. 82), Ducks, and Geese. 



The hyoid is composed of basal elements, the anterior of 

 which, usually composed of two portions, lies in the tongue ; 

 and of two short, anterior, and two long, posterior, cornua, 

 which are never united with the periotic region of the skull, 

 and commonly remain quite free. In some of the Wood- 

 peckers, however, the long posterior cornua are immensely 

 elongated, and curved upward and backward over the skull 

 (the frontal bones being grooved to receive them), and their 

 free ends are inserted between the ascending and maxillary 

 processes of the right premaxilla. 



The pectoral arch presents a long, narrow, and recurved 

 scapula {Sc. Fig. 84|-), without any suprascapula ; and a cora- 

 coid (Co.), fitted by its proximal end into the groove in the 

 antero-lateral edge of the sternum. The inner ends of the 

 coracoids occasionally overlap, as in Xiacertilia ; otherwise, the 

 shoulder-girdle is unlike that of any of the Reptilia^ except the 

 Pterosaurla. The coracoid is usually completely ossified, and 



Fio. &4i —The right scapula {Sc!) and coracoid {Co.') of a Fowl: gZ, the glenoidal cavity, 

 /, the right clavicle, or right half of the furculum ; hp, the hypocleidium. 



