xrn 



PHYLUM CHORDATA 



311 



7T7 



FIG. 974. Pectoral arch and sternum of Lacerta agilis. 

 el. clavicle ; cor. coracoid ; ep. cor. epicoracoid ; epis,t. 

 episternum ; tjlen. glenoid cavity for head of humerus ; 

 pr. cor. procoracoid ; r.l rA first to fourth sternal ribs ; 

 sc. scapula; st. sternum; nupra.se. suprascapula. 

 (After Hoffmann.) 



from their articulation with the humerus downwards and slightly 



forwards, while the manus has the digits directed forwards and 



outwards. When the 



limb is extended at 



right angles to the 



long axis of the trunk, 



it presents, like that 



of the Frog, dorsal 



and ventral surfaces, 



and pre-axial and post- 

 axial borders, In this 



position the radius is 



seen to be pre-axial, 



the ulna post-axial. 



In the natural posi- 

 tion the pre-axial 



border of thejmmerus 



is external, and the 



distal end of the fore- 

 arm is rotated in such 



a way that, while the 



pre-axial border looks 



forwards and outwards 



at the proximal end, 



it faces directly inwards at its distal end, the manus being rotated 



so that its pre-axial border looks inwards. 



The humerus is a long bone consisting of a shaft and two ex- 

 tremities, each of the latter being formed 

 of an epiphysis of calcined cartilage, the 

 proximal rounded, the distal (trochlea) 

 pulley-like, with two articular surfaces, one 

 for the radius and the other for the ulna. 

 The radius is a slender bone consisting, 

 like the humerus, of a shaft and two epi- 

 physes ; the distal extremity has a con- 

 cave articular surface for the carpus, and 

 is produced pre-axially into a radial 

 styloid process. The proximal end of the 

 ulna is produced into an upwardly directed 

 icranon : the distal end 

 bears a convex articular surface for the 

 carpus. The carpus (Fig. 975) is com- 



fl>e p metacarpais. rin (From F w^ posed of ten small polyhedral or rounded 

 S!) eim>s Comparati " e Ana ~ carpal bones. These consist of a proximal 



row containing three, viz., the radiale (r), 



ulnare (u), and intermedium (i), of a centrale (c), and of a distal row 



of five (1-5} ; with an accessory or pisiform (\) bone attached 



u 2 



FIG. 975. Carpus of Lacerta - l ^ rnc . ( , (i a flip 

 agilis, (left) from above. /,'. 

 radius ; U. ulna ; c. centrale ; 

 i. intermedium ; r. radiale ; u. 

 ulnare : 1 5, the five distal 



