THE TECTORAL GIRDLE. 



37 



a. The sternum proper (Fig. 24 //.s.), a rod of cartilage 

 enslieatlied in bone^ broader in front and narrower behind. 

 To its posterior extremity is attached 



h. The cartilaginous xiphistemum (Fig. 24 lis), a plate^ the 



shape of which is best understood by referring to Fig. 24, and 



the structure of which is similar to that of the episternum. 



3. Tlie epicoracoids ^ lie between the ei^isternum and the sternum 



proper : they are a pair of narrow cartilages, closely applied to 



each other and placed between the ventral ends of the precoracoids 



and coracoids, see p. 40. 



IV. THE BONES OF THE ANTEEIOR EXTKEMITY. 



A. Boxes of the Shoulder-giudle. 



The shoulder-girdle of the frog (Fig. 25) consists of four bones, 

 two in the upper or scapular portion, and two in the lower or 

 eoracoid portion. 



1. The scapular portion. Fig- ^i- 



a. The suprascapula, jkits snjjra- 

 scapiiiaris scapulae^ scapula siijperior 

 s. omollta (Figs. 25 /, 26, 27). 



This forms the upper, thinner por- 

 tion. It is trapezoid in shape, its 

 narrowest, thickest, and lowest 

 border articulating with the sca- 

 pula. The remaining three borders 

 are free; the posterior and supe- 

 rior borders are very considerably 

 thinned out, the inferior surface 

 is curved towards the ventral 

 surface. Only the thin upper and 

 hinder borders (////) are of hyaline 

 cartilage ; the middle portion {co) 

 consists of calcified cartilage ; the 

 lateral part (0) and the anterior border {0) of true bone. 



The bony part forms a thin plate striated both radially and 



' Dugës, I.e., p. 61, regards the cartilaginous laminae as os epldernale and proc. 

 xiphoidetis, and the two bones e.g. and h.s. (Fig. 24) as sternum. 



Slinuldei-giidle of the frog in transverse 

 section, diagraniniîitic. 

 c Connecting cartilage. 

 c' Epicoracoids. 

 H Cla\'icles. 

 h Humerus, 

 ^v Scapula. 

 s' Suprascapula. 

 ss Ai'ticulation of these two. 

 V Vertebra. 



