204 Annals ok the Carnegie Museum. 



Viewed anteriorly, the outer condyle is the broader, extends higher 

 on the shaft, but projects no further in front than the inner one. This 

 latter, slightly encroaching on the intercondyloid space, is excavated 

 by a well-defined subelliptical pit, which is better marked in the Night 

 Herons, though present in the Ardcime generally. 



Viewed from behind, these condyles of the tibia in Ardea mount 

 to points about opposite each other on the shaft. There, however, 

 the inner condyle is the broader, and rather more prominent above. 



Upon lateral aspect these condyles are uniform in outline with the 

 convex surfaces below; and from above, downwards, the outer is the 

 deeper of the two. 



In my memoir on the Osteology of the Gallin^E (in MSS. ) I de- 

 scribe the method of ossification of the cnemial crest of the tibia in 

 the young of CeJitrocercns iiropliasianus and give a figure showing this 

 development, which, in brief, consists in a large osseous segment en- 

 grafted upon the bone, at the future site of the cnemial crest and 

 upper halves of the pro- and ecto-cnemial ridges, all of which it forms, 

 but leaves no trace of such a development in the adult fowl. 



My only regret is that I have not at this moment the proper material 

 to investigate whether or no a like method of development goes on in 

 the young of the Herons. 



As for the distal extremity of this bone, it also has received no little 

 attention generally, but in particular the young of our present subject 

 has been ably investigated at the hands of Professor Morse. 



It was through his studies of the tibia and tarsus of immature indi- 

 viduals of various spcies of Ardea that this distinguished zoologist 

 was principally enabled to demonstrate the presence of the inter- 

 medium in the Class birds. Professor Morse's researches have proven, 

 I think, beyond doubt, that the " ascending process of the astralagus " 

 of Huxley agrees with the " pretibial " of Wyman. Further, this 

 segment ossifies from a separate center of ossification, and as such con- 

 stitutes in the avian tarsus a third bone of the proximal row, which 

 corresponds with the interi)iediuin of the Reptilia as described by 

 Gegenbaur. No one would suspect the presence of any such bone 

 in the adult, in any of the Ardeince, it having been completely ab- 

 sorbed by the tibia, and every vestige of its original limits obliter- 

 ated. 



Thtjidiihi of the Great Blue Heron is a very much aborted bone, 

 not only when it is compared with that bone as it is found in many 



