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. When 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, Ocydromus, Cariama, Didus, Carpophaga, many Psittact and 
Striges, Musophagidx, Buceros, Alcedo, Rhamphastos 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 
Hypocleidium, 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, asin many Tudbinares, 
Steganopodes, Ardex, Ciconix, Gruidx, Striges, Gypogeranus, Cuculus 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, while 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 Dromzus, Casuarius, many of the Psittaci—as Stringops and 
nearly all the Platycercinx, Capito and, among the Passeres, Atrich- 
ornis. In extreme cases both clavicles are wholly lost, as in Din- 
ornis, Apteryx, Struthio, Rhea and Mesites. 
THe ANTERIOR Limss 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 which may be conveniently expressed as follows :— 
Clavicle connected with— 
(1) Precoracoid process only :—Hesperornis. 
(2) Preecoracoid chiefly, hardly with Acromion :—Zatitz. 
(8) Acrocoracoid only :—many Alcidx, Steganopodes, Ardex, Ciconix, Gruide, 
Vultur, Gypaetus, Cathartes, Cypselus. 
(4) both Precoracoid and Acrocoracoid:—some Lari, Limicolw, Gruidex, 
Rallide, Turnix, Opisthocomus, Columbex, Psittaci, Striges, Trochilus, 
many Picariz and Falconidz. 
(5) Acrocoracoid and Acromion— 
(a) attached to the anterior margin of the Acromion :—Sphenisci, 
Tubinares, Crypturt, Galline, Psittaci 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, Alecdinidx 
Meropidx, Coractide, Todidx and.all Passeres. 
