XIII 



PHYLUM CHORDATA 



363 



ret 



Craniates. There is a pair of stout, pillar-like coracoids (cor.) 

 articulating with deep facets on the anterior border of the sternum 

 and directed upwards, forwards, and outwards. The dorsal end of each 

 is produced into an acrocoracoid process (acr. cor ), and below this, to 

 the posterior aspect of the bone, is attached by ligament a sabre- 

 shaped scapula (scp.) which extends backwards over the ribs, and 

 includes, with the coracoid, 

 an acute angle, the coraco- 

 scapular angle. The glenoid 

 cavity (gl. cv.) is formed in 

 equal proportion by the two 

 bones ; internal to it the 

 scapula is produced into an 

 acromion process. In front of 

 the coracoids is a slender 

 V-shaped bone, the furcula 

 (fur.) or " merrythought," the 

 apex of which nearly reaches 

 the sternum, while each of its 

 extremities is attached by 

 ligament to the acromion and 

 acro-coracoid processes of the 

 corresponding side, in such a 

 way that a large aperture, the 

 foramen triosseum (f. trs.) is 

 left between the three bones 

 of the shoulder-girdle. The 

 furcula is a membrane bone 

 and represents fused clavicles 

 and interclavicle. 



Equally characteristic is the 

 skeleton of the fore-limb. The 

 humerus (Fig. 975, hu.) is a 

 large, strong bone, with a 

 greatly expanded head and 

 a prominent ridge for the in- 

 sertion of the pectoral muscle. 

 In it, as in all the other long 

 bones, the extremities as well 

 as the shaft are formed of 



true bone. The radius (ra.) is slender and nearly straight, the 

 ulna stouter and gently curved. There are two large free carpals, 

 a radiale (ra. r ) and an ulnare (ul.'), and articulating with these is a 

 bone called the carpo-melacarpus ( cp.mtcp.) consisting of two rods, 

 that on the preaxial side strong and nearly straight, that on the 

 postaxial side slender and curved, fused with one another at both 

 their proximal and distal ends; the proximal end is produced, 



ra' 



ph.* 



Pi<;. 075. Columba livia. Skeleton of the 

 left wing. cp. intcp. carpo-metaearpus ; /<. 

 humerus ; ph. 1, phalanx of first digit ; ph.2', 

 ph. 2", phalanges of second digit ; ph.-3, phalanx 

 of third digit ; pn. Jor. pneumatic foramen. 

 RA. radius; ra. radiale; Ul ulna; ul. ulnare. 



