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Prof. W. K. Parker. 



[Mar. 22, 



a great height above their former selves, may have taken place in the 

 past on a grander scale, and with centuries for days. 



However it came about, the Saururous (long -tailed) forms have 

 become Nothurous, have a mere bastard tail or stump. Yet this mor- 

 phological feat is performed in the transformation of any Tadpole 

 in "a month of days," hence the real difficulty does not lie with 

 Nature, but with us. 



But in studying the abortive chevron-bones of birds we shall find 

 that these high and marvellously transformed types are not short- 

 tailed, if we consider number merely ; it is the peculiar contraction 

 and packing — consolidation — these segments have undergone that 

 make them to differ so greatly from Reptiles and Saururous birds.* 



In the Common Swan (Gygnus olor), behind the four true sacrals 

 there are ten " urosacrals " fused with the long post-ilia ; then come 

 seven simple, and one compound, bone, composed in the cygnet of five 

 bony segments and an unossified rudiment behind, six altogether. 

 We thus get, even allowing for four sacrals, twenty-three vertebrae, 

 more or less developed behind the outgoing sacral nerves, whilst the 

 Archceopteryx appears to have had only twenty-one caudal vertebrae 

 (See ' Zool. Soc. Proc.,' 1863, p. 517). 



Now of these post-sacral vertebrae of the Swan nearly the hinder 

 half have rudimentary intercentra. These are very small, those in 

 the middle of the series being the largest. In the cygnet about a 

 month after hatching, the first is beneath the third movable 

 joint, and the last under the last cartilaginous interspace but one, in 

 the series of imperfect segments that form the "ploughshare bone;" 

 thus there are eight in all. 



But there are intercentra at the other end of the chain ; these 

 I have studied in the Cygnet, in the ripe embryo of the Mooruk 

 (Casuarius bennettii) and in various other birds, especially Carinatae ; 

 whilst my son (T. J. Parker) has worked them out in the embryo of 

 Apteryx. In these embyo, and young birds, there are always found 

 the following osseous centres in the atlas and axis, namely, a pair for 

 the neural arch of each vertebra, and one for the so-called " body " of 

 the atlas, one for the odontoid process of the axis, and two for the 

 body of the axis, not right and left, but one before the other. 



The osseous centre in the cartilaginous odontoid process is strung 

 upon the notochord, like the rest of the centra ; it is the specialised 



* This subject has long been on my mind ; lately Dr. Baur unearthed an almost 

 forgotten paper of mine on the tail of modern birds. See his " W. K. Parker's 

 Bemerkungen liber Archaeopteryx, 1864, und seine Zusammenstellung der hauptsach- 

 lichsten Litteratur iiber diesen Yogel," ' Zool. Anzeiger,' No. 216, 1886. My 

 earliest paper on this special point was read at the Zoological Society on December 8, 

 1863. See ' Zool. Sue. Proc.,' 1863, pp. 511—518. It was "On the Position of the 

 Crested Screamer (Palamedea \_Chauna] chavaria) ." 



