MORPHOLOGY OP OPISTHOOOMUS CRISTATUS. 77 



both ends ; the same thing is seen in Corythcdx ; in Oinsthocomus there is a clear space 

 between these parts, right and left ; this is also seen in the Turnicidae. Even this part 

 of the skeleton, therefore, like the rest, suggests a low ornithological position for this 

 bird, and justifies the use of the term archaic as applied to it. 



VIII. The Hind Limb of Opisthocomus cristatus. 



The leg of Ojpisthoconms in the 1st stage is strong and rather stout (PI. VII.) ; its 

 long elements have a considerable ectosteal sheath ossifying the solid cartilage. The 

 parts of this limb differ little from those of an embryo of the Common Fowl at this 

 stage ; we shall find a few notable differences, showing that we are, here, at the parting 

 of the ways. The relative length of the main divisions of the limb, at this stage, is 

 very similar to what is seen in a large number of those Carinatse that have moderately 

 long legs, whether they are Perchers, Walkers, or Runners. Measured from the chief 

 points of flexure, these parts have now their length as below : — 



Femur. Tarso-tibia. Tarso-metatarsus. Srd toe. 



11 millim. 13 millim. 8 millim. 14 millim. 



The ends of the large cartilages are still unossifled, and they will not be finished by 

 epiphyses, except in the case of the cnemial process of the tibia : in a few Cuculine 

 birds the top of the fibula has a small epiphysis, but that is rare in the Carinatse ; in 

 the fore limb, in some rare cases, sometimes the radius and sometimes the ulna has an 

 epiphysis. The cnemial process is not large ; the fibula {fb.) has shrunk to half the 

 length of the tibia {t.); the tibia is quite distinct from the proximal tarsals [tb., 

 fbe.). All the true tarsal elements are free from bony deposit at present (Pis. VII. & 

 X. fig. 10). Tliere is some contention as yet as to the true nature of these segments ; 

 but, after much labour and thought, my own mind is made up as to their morpho- 

 logical meaning. When I first asked whether or no the lower part of the tibia v/as an 

 epiphysis or " the homologue of the Mammalian astragalus " (" On Balceniceps rex,'" 

 Tr. Z. S. vol. iv. p. 343), I was still in the dark as to the nature of the " sesamoid os 

 calcis." Since then, several anatomists, notably Gegenbaur and Huxley, have worked 

 at this part of the bird's skeleton. 



One of the most valuable pieces of work on this subject is Dr. Morse's paper " On 

 the Intermedium in Birds " (Ann. Mem. Boston Nat. Hist. 1880), though his views, 

 which are mine also, have been controverted by Dr. G. Baur \ 



In a paper (ready for publication), my son. Prof T. J. Parker, also holds the same 

 views as Dr. Baur ; his observations have been made on the development of the 

 Apteryx. I am perfectly convinced of the truth of Dr. Morse's views. Nevertheless 

 I believe that there are only two morphological elements in the proximal tarsal series — 

 an astragalus, or tibiale, and a calcaneum, or fibulare. The so-called sesamoid, or 



^ See his paper, " Der Tarsus der Vogel und Uinosaiirier," Morph. Jahrb. Bd. viii. pp. 417-456, Taf. 19, 20. 



m2 



