end of the tibia and tarsus of the opossum remain distinct, 

 as do those of the other long bones of the Umb. 



The function of the fibulare is of interest; it extends down 

 and back to form the heel. In the anterior hmb, the pisi- 



TABLE 6-3 



SYNONYMY OF NAMES APPLIED TO THE BONES OF 

 THE ANKLE REGION, THE TARSALS, OF TETRAPODS 



cleithrum 



forme has the same function. The fibulare of the mammal 

 is peculiar in that it does not articulate with the fibula. The 

 astragalus is apparently a compound bone as is observed in 

 the primitive reptile. This will be discussed later. 



In comparing the anterior and posterior limbs we find 

 that they are very similar in the units composing them. This 

 similarity represents a kind of serial homology which must 

 be entirely or in part functionally determined. 



Reptile and bird 



Pectoral appendage In Sphenodon or the lizard, the girdle 

 consists of three dermal elements: the clavicles of either 

 side, jointed with a median interclavicle (Figure 6-48). The 

 chondral elements of either side include a dorsal scapula 

 fused with a ventromedial procoracoid. The use of pro- 

 coracoid here will be explained when fossil reptiles are 

 examined. The scapula generally has a process (the acro- 

 mion process of the mammal spine) that extends out to the 



scapula 



interclavicle 



clavicle 



clavicle, 

 procoracoid 



procoracoid 

 corocoid 



coracoid 

 nterclavicle_ 



D ORNITHORHYNCHUS 



scapula 



clavicle 



interclavicle 



SEYMOURiA 



B DIMETRODON C 



clavicle 



E TRICHOSURUS 



clavicle. 



scapula 



interclavicle 



F SPHENODON 



TUPINAMBIS 



H 



ALLIGATOR 



Figure 6-48. Pectorol girdles of reptiles and mammals as seen in lateral and ventral views (C). 

 A, Seymouria; B and C, Dimetrodon; D, Ornithorbynchus; E, Tricfiosurus, a shrew; F, Sphenodon; 

 G, Tupinomb/s; H, A//iga(or. (A, B, C after Romer, 1 956; D; after Vialleton; E, after Broom) 



BILATERAL APPENDAGES 



173 



