PHYLUM CHORDATA 



469 



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 ; in- 

 ternal 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 aper- 

 ture, the foramen triosseum 

 (f trs) is left between the 

 three bones of the shoulder- 

 girdle. The furcula is a mem- 

 brane bone and represents 

 fused ' clavicles and inter- 

 clavicle. 



Equally characteristic is the 

 skeleton of the fore-limb. The 

 humerus (Fig. 281, hu) is a 

 large, strong bone, with a 

 greatly expanded head and 

 a prominent ridge for the in- 

 sertion ol the pectoral muscle. 

 The radius (ra) is slender 

 and nearly straight, the ulna 

 stouter and gently curved. 

 There are two large free car- 

 pals, a radiale (ra!) and an itlnare (uf), and articulating 

 with these is a bone called the carpo-metacarpus (cp. mlcp), 

 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 



Fig. 282. — Columba livia. Left manus 

 of a nestling. The cartilaginous 

 parts are dotted, cp. I, radiale; 

 cp. 2, ulnare ; mcp I. 2,3, meta- 

 carpals; ph. I, phalanx of first digit; 

 ph. 2, ph. 2', phalanges of second 

 digit; ph. j, phalanx of third digit; 

 ra, radius; id, ulna. (From 

 Parker's Zootomy.') 



