THE FROG 31 



is termed the anterior or pre-axial border of the limb, and the other 

 the posterior or post-axial border. 



The fore-limb is attached to the body by means of the pectoral 

 girdle, which consists of a bony framework, almost completely 

 encircling the body, but incomplete on the dorsal side. Each half 

 is divided into two portions by the glenoid cavity, a hollow depression 

 lined by articular cartilage, into which the head of the humerus fits. 

 The dorsal, scapular part, consists of two elements, a fairly stout 

 cartilage bone, the scapula, which forms part of the glenoid cavity, 

 and a thinner wider bone, the supra-scapula, situated more dorsally. 

 The supra-scapula never completely ossifies, and its dorsal edge is 



hh 

 F IG . 6. A, Left fore-limb Rana'. B, Left half pectoral girdle Rana. 



a., articular knob of humerus ; c.f., coracoid foramen ; cl., clavicle ; co., coracoid : c.r., con- 

 dylar ridge ; d.c., distal carpalia ; d.r., deltoid ridge ; ec., epicoracoid ; es,, episternum ; /.&., 

 facet for articulation with head of humerus ; h., humerus ; h.h., head oi humerus ; m., meta- 

 carpalia ; ms., mesosternum ; os., omosternum ; ^p., phalanges ; r ., radiale ; r.u., radio-ulna ; 

 sc., scapula ; s.s., supra-scapula ; ., ulnare ; xs., xiphisternum ; /., ist metacarpal ; II. -V ., 

 digits. 



always formed of cartilage. The ventral part of the girdle is known 

 as the coracoid portion. From the anterior corner of the glenoid 

 cavity a narrow rod, the pre-coracoid, runs inwards toward the 

 middle line, not quite meeting its fellow from the opposite side. 

 Actually only a very narrow strip of this is visible, because a thin 

 bone, the clavicle, is wrapped round it. The clavicle is the only 

 membrane bone in the appendicular skeleton, and may or may not 

 be represented in ourselves by the collar bone. The posterior ventral 

 part of the glenoid cavity is formed by the coracoid bone, which 

 passes inwards and backwards, leaving a space, the coracoid foramen, 

 between it and the clavicle. Its inner end is expanded, but, like 

 the pre-coracoid, does not touch its fellow of the other side. The 



