I.]] THE FROG. 69 



b. The paired elements. Flatten out the whole on one 

 side, so as to obtain a lateral view. In the region 

 of the glenoid fossa there will be seen a sharp line 

 of demarcation between a dorsal scapula segment; 

 and a ventral coracoid segment, the middle area of 

 which is fenestrate (coracoid fontanelle). 



a. The scapula segment; subdivided into a thin ex- 

 panded partially ossified dorsal portion (supra 

 scapula) and a stouter bony piece (the scapula) 

 which furnishes the dorsal half of the glenoid 

 fossa. 



/}. The coracoid segment; largely ossified, and com- 

 posed of a smaller anterior clavicle, and a 

 stouter posterior coracoid, the latter furnishing 

 the ventral half of the glenoid fossa. 



c. The median elements. 



a. The xiphisternum ; a median cartilage, en- 

 sheathed in bone, abutting against the applied 

 ends of the coracoids. It expands posteriorly 

 to form a heart-shaped plate, notched from 

 behind (xiphoid process). 



/?. The omosternum, a slender cartilage ensheathed 

 in bone, similarly related in front. It also ends 

 in a cartilaginous expansion. 



It is doubtful if the above really represent 

 sternal elements, especially in the case of the 

 anterior one. 



The skeleton of the fore-limb. (Cf. Sect. A. 2. c.) 

 a. The arm-bone (humerus). 



a. A somewhat cylindrical bone, composed of a 

 middle shaft with an articular expansion at each 

 end. 



