858 SKELETON 



a very marked way in Fregata, one of the most powerful fliers of the 

 world (Frigate-bird, pages 293, 294). 



The Clavicles when united, as is generally the case, are known 

 as the FURCULA (page 296). Their dorsal extremity may be vari- 

 ously attached to the Scapula and Coracoid or to one only,^ and 

 here is a wide field for variation, which seems however constant 

 enough in the different groups. AVhen Clavicles do not fuse at 

 their ventral extremity, they are occasionally joined by semiossified 

 cartilage or fibrous tissue, admitting of slight motion, as in Hesper- 

 ornis, Ocyclromus, Cariama, Didus, Carpophaga, many Fsittaci and 

 Striges, Musophagidx, Buceros, Alcedo, EhampJiasfos and Capito ; but 

 in by far the greater number of Birds the Clavicles are drawn out 

 at their symphysis into a median projecting blade, knob or rod, the 

 Hypodeidmm, which frequently ossifies from a centre of its own. 

 The hypocleidium often touches the keel of the Sternum, leading to 

 a syndesmosis or even synostosis therewith, as in many Tubinares, 

 Steganopodes, Ardese, Ckonix, Griddse, Striges, Gijpogeranus, Cucidus and 

 Buceros. The peculiar connexion in Opisthocomus has already been 

 mentioned (HoACTZiN, page 423). In a considerable number of 

 Birds of various groups the Clavicles are more or less degenerated, 

 their dorsal portion being alone retained, wliile the ventral is repre- 

 sented by a long ligament extending to the keel of the Sternum. 

 This condition exists both in Birds that fly and those that cannot, 

 as in Dromxus, Casuarius, many of the Psittaci — as Stringops and 

 nearly all the Platycercinse, Capito and, among the Passeres, Atrich- 

 ornis. In extreme cases both clavicles are wholly lost, as in Din- 

 amis, Apteryx, Struthio, Rhea and Mesites. 



The Anterior Limbs or Wings are composed of three principal 

 portions: (1) the Humerus, of which enough has been already 



1 The connexion of Coracoid, Scapula and Clavicle with each other is subject to 

 many modifications, the chief of whioh may be conveniently expressed as follows : — 

 Clavicle connected mth — 



(1) Praecoracoid process only : — Hcsperornis. 



(2) Prtecoracoid chiefly, hardly with Acromion : — Ratitm. 



(3) Acrocoracoid only : — many Alcidse, Steganopodes, Ardem, Ciconiae, Gruidee, 



VuUu7; Gypaetus, Cathartes, Cypsclus. 



(4) both Praecoracoid and Acrocoracoid : — some Lari, Limicolee, Gruidx, 



Rallidx, Turnix, Opisthocomus, Coluvibse, Psittaci, Striges, TrochiluSy 

 many PicarisB and FalconidsB. 



(5) Acrocoracoid and Acromion — 



(a) attached to the anterior margin of the Acromion : — Sphenisd, 



Tubinares, Grypturi, GaUinae, Fsittaci and many others. 



(b) reaching further back, beyond the dorsal margin of the Acromion, and 



even over the neck of the Scapula : — Colymbus, Podicipes, Anseres. 



(c) attached to the inner surface of the Acromion : — Pici, Alcedinidm, 



Meropidas, Coraciidse, Todidae and all Passeres. 



