xiii.] THE FROG. 121 



composed partly of bone, partly of cartilage. Note 

 the hollow (glenoid fossa) with which the fore-limb 

 articulates. 



a. The sternum : situate in the ventral median line 

 and made up of several parts: beginning behind 

 we find 



a. The xiphistern um ; a thin cartilage, wide 

 behind, narrow in front, where it passes 

 into 



(3. A median cartilage ensheathed in bone, the 

 sternum proper. The anterior end of the 

 sternum unites with the posterior and inter- 

 nal angles of the coracoids (b. y), the inner 

 edges of which meeting in the middle line 

 separate the sternum from 



y. The omostcnntm, consisting of a slender, flat- 

 tened bone, terminated in front by an ex- 

 panded cartilage. The posterior end arti- 

 culates with the praecoracoids and the clavi- 

 cles. 



b. The shoulder-girdle: beginning dorsally, it ex- 

 hibits on each side 



a. A thin expanded dorsal portion, partly car- 

 tilaginous, partly ossified : the supra-scapula. 



ft. Next a bony segment the scapula, the pos- 

 terior inferior edge of which is excavated by 

 the glenoidal fossa. 



The ventral parts of the shoulder-girdle, which 

 lie between the two scapulae, meet in the mid- 

 dle line; the part on each side is subdivided 



