EGG-LAYING MAMMALS, OR MONOTREMES. 169 



as the Anomodonts, or Anomodontia. In Amphibians 

 (Frogs, &c.) there is, however, likewise a distinct pre- 

 coracoid, which in some extinct types not improbably 

 approximated to the form 

 shown in Fig. 50 ; although 

 in frogs the precoracoid 

 forms a simple rod-like 

 bone. 



We find, therefore, that 

 the only known animals 

 possessing both a coracoid 

 and a precoracoid as sepa- 

 rate elements distinct from 

 the shoulder-blade* are 

 the Monotreme Mammals, 

 the Anomodont Reptiles, 

 and the Amphibians ; and 

 since we have shown that 

 in other respects the Mo- 

 notremes are to a con- 

 siderable extent interme- 

 diate between Reptiles and 

 other Mammals, there 

 arises a strong presump- 

 tion that the Echidna and the Duck-bill are the last 

 i 



remnants of a group of animals which were veritable 

 connecting links between Mammals, Reptiles, and 

 Amphibians. Now among the Anomodont Reptiles 



FIG. 50. The right side of part of the 

 shoulder-girdle of an Anomodont 

 Reptile, ae, shoulder-blade ; ab, pro- 

 cesses of do.; cor., coracoid bone; 

 p. cor., precoracoid bone ; </l, cavity for 

 head of arm-bone. The shaded portion 

 is from an Indian and the unshaded 

 from an African specimen. 



* In adult Monotreines the coracoid unites by bone with the 

 shoulder-blade. 



