OCR Text |
Show 1905.] OSTEOLOGY OF THE EURYLiEMID/E. 47 is long, slender, gently arched, and bears a large hypocleideum, roughly quadrangular in form, and articulating with the anterior edge of the carina. The free ends of the furcula are expanded to form flat plates articulating with the acrocoracoid, procoracoid, and acromion process of the scapula (text-fig. 14), thus enclosing the foramen triosseum. In the form of the sternum and shoulder-girdle the Eurylsemidse closely resemble the Cotingidse, especially in the form of the spina externa, which is simple, and thereby differs from the typical Passerine form wherein it is forked. In the Eurylsemidae this process is more or less spike-shaped, whereas in the Cotingidse it appears to be generally flabellate. In Chasmorhynchus the posterior sternal notches are not so deep as in the Eurykemidse. The hypocleideum articulates nearer the antero-ventral angle of the carina; and the coracoids do not develop the internal basal flange found in the Eurykemidse. Text-fig. 14. Portion of the shoulder-girdle of Calyptomena, to show the meeting-point of the scapula, coracoid, and clavicle, forming the inner wall of the foramen triosseum. sc., scapula; ac., acrocoracoid ; f , furcula. In the relations of the articulations between the procoracoid, furcula, and scapula, where these unite to form the foramen triosseum, the Eurykemidse are distinctly Passerine, though this arrangement also obtains among the Picidse-a fact of some significance. In Calyptomena, for instance, the acromion process of the scapula extends downwards along the anterior border of the free edge of the procoracoid, and affords an articular surface cephalad, for the posterior angle of the expanded free end of the furcula. In Chasmorhynchus this articulation for the fui'cula is markedly increased; and this increase apparently reaches its maximum in the Corvidae, where the acromion forms a long beam-like roof to the foramen triosseum, and a very extensive articular surface for the furcula. |