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FRANK BLAIR HANSON 



with the largest number and most intimate union of ribs to 

 breast bone the sternum is but feebly developed; while, on the 

 other hand, some of the largest sterna have the fewest number 

 of ribs and feeblest connection of the two; or, as in Chirotes, a 

 fully developed sternum showing the three typical divisions is 

 present, but no ribs reach the sternum — conditions hardly to be 

 expected if the ribs contribute the sternal materials. 



The following table is a composite one from several authors and 

 shows but a few of the numerous forms they lisl . 



Chirotes canaliculatus 



Anguis fragilis 



Chamaeleo pumilis 



Monitor dracaena 



Draco viridis 



Stellio vulgaris 



Calates pictus 



Iguana tuberculata 



Crocodilus acutus 



Gavialis schlegelii 



4. Birds 



Birds, although not in the line of descent of the mammals and 

 also having a sternal apparatus highly modified for purposes of 

 flight, are still not difficult to bring into line in this argument. 

 However, it is hardly necessary to do this as we are following 

 successively more complex and highly differentiated groups in 

 their phylogenetic course. Nevertheless, to show that there is 

 nothing contradictory to our thesis among the birds, one figure 

 of a bird is introduced. This is Vanellus cristatus (fig. 33) and 

 is of a stage at the end of the first third of the incubation period. 

 Parker's remarks upon this sternum give us the pertinent facts: 

 "The longitudinal bands are long and wide, and in great contrast 

 to the very slender pairs of ribs attached to them. On the other 

 hand, a transverse cleft between the epicoracoids and the antero- 

 lateral margins of the longitudinal bands would give us the con- 



