26o 



VERTEBRATE SKELETON 



with the humerus (not paralleled elsewhere in mammals) and with the prester- 

 num. Talpids also have short and quadrangular clavicles and humeri ; elsewhere 

 the clavicle is long and slender. 



Chiroptera (fig. 277) have a large oval scapula, the spine near the anterior 

 border, with one or two small ridges (accessory spinae) behind it, the spine itself 

 being short and rather high. The acromion is large and the long curved coracoid 

 is sometimes forked at the tip. The strong clavicle extends from sternum to 

 scapula, making a strong brace against the action of the large pectoral muscles. 

 Edextata. — The pectoral girdle of Edentates varies considerably. In the 

 Tubulidentata the scapula is normal, the clavicle strong and curved, and has 

 the ventral end expanded. Pholidota have a broad scapula, rounded dorsally, 

 with a suprascapular cartilage, and a spine rather nearer the posterior than the 



anterior border. The acromion is small, 

 the coracoid greatly reduced and no 

 clavicle is present. Xenarthra (fig. 278) 

 have a broad scapula, often with an 

 accessory spine, an acromion, slender in 

 Myrmecophaga, long and curved in arma- 

 dillos, and often with a facet on the 

 inner surface for the humerus; in sloths 



Fig. 277. — Pectoral girdle, ribs and 

 sternum of Eumops californicus. cl, 

 clavicle; co, coracoid; g, glenoid fossa; 

 w, mesosternum; p, presternum; r, 

 ribs; sc, scapula; ss, suprascapula; x, 

 xiphisternum. 



Fig. 278. — Scapula of Dasypus 6-cinctus. 

 a, acromion; co, coracoid; cl, clavicle; s, 

 spina; sc, scapula. 



the spine rises only from the ventral part of the scapula, and there is no second- 

 ary spine. Many Xenarthra have a marked incisure in the anterior border of the 

 scapula just dorsal to the coracoid, which is converted into a coraco-scapular 

 foramen in Myrmecophaga and sloths by the union of the precoracoid part of the 

 process with the anterior border of the scapula. The clavicle is small or absent 

 in anteaters, well developed in armadillos. and the two-toed sloth, reduced in 

 other sloths. 



RODENTIA usually have a long slender scapula with a long acromion (espe- 

 cially long in Myopotamus). The coracoid is always small and the clavicle varies 



