THE PECTORAL GIRDLE. 



37 



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

 ensbeathed in bone, broader in front and narrower behind. 

 To its posterior extremity is attached 



Ij. The cartilaginous xiphisternum (Fig. 24///), 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. The epicoracoids 1 lie between the episternum 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 ANTERIOR EXTREMITY. 



A. BOXES OF THE SHOULDER-GIRDLE. 



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. ^5. 



a. The suprascapula. par* xnpr.i- 

 Kapulari* scapulae, scapula #//_/,< 

 s. omolita (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 - 

 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 (o) and the anterior border (</) of true bone. 



The bony part forms a thin plate striated both radially and 



Sluiulder-girdle of the frog in transverse 



section, diagrammatic. 

 Connecting cartilage. 

 Epicoracoids. 

 Clavicles. 

 Humerus. 

 Scapula. 

 Supraseapula. 

 Articulation of the<' twn. 

 Vertebra. 



1 Duges, I.e., p. 61, regards the cartilaginous laminae as os epitteniale and proc. 

 xiphoideus. and the two bones e.s. and h.y. Tig. .24; as >ttrnum. 



