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PROF. G. B. HOWES AND MR..H. H. SWINNERTON ON THE 
On examination of trausverse sections through the developing vertebral column 
of Sphenodon at Stage P, at which the parts of the cartilaginous vertebre are as yet 
undifferentiated, the tissue giving rise (Pl. I. figs. 5 & 4) to the paired intercentra 
(i.p.')—which, it will be remembered, are the first, and at this stage the only components 
of the vertebral column recognizable—is seen to be continuous with that differentiating 
into the ribs (7.ed.). Figs. 3 and 4 represent the first and sixth sections across an 
individual caudal segment; and comparison of those which intervene has shown us 
that even here, when the vertebral body is not yet differentiated, the disposition of the 
proximal end of the rib is oblique, involving ventrally and anteriorly the intercentrum, 
dorsally and posteriorly the region of the future centrum and arch. Comparison with 
the adult cervical rib reveals a close similarity of relationship; and since with later 
development the connection with the intercentrum is lost, the primary relationship of 
the rib is proved to be intervertebral. 
Cope in 1878 first drew attention ! to the existence in certain Permian Pelycosauria 
of a two-headed condition of the rib, with accompanying intercentral articulation of 
the capitulum; and Baur, eight years later, in his afore-mentioned paper on the 
cervical ribs of Sphenodon (prompted by Cope’s announcement), sought to emphasize 
the importance of this. Cope, immediately afterwards, in dealing with the structural 
resemblances between these creatures, prompted by Hofmann’s brilliant generalization 
afore-mentioned, penned the remarkable paragraph?: ‘“'The passage of time has 
seen in the Reptilia generally ” a modification ‘in the mode of attachment of the 
rib,” in which, “in passing from front to back, the intercentral articulation is 
lost, and finally the head of the rib disappears.” The facts we have just described 
render this well-nigh prophetic; and it remains to be ascertained how far the sup- 
position, deduced from the study of longitudinal sections alone, that the ribs of the 
Amniota, and of the Reptilia in particular, arise in exclusive relationship to the 
transverse process, centrum, or arch, will stand the test of examination in other 
planes, and, as deduced from that of developmental stages at which chondrification 
is more or less advanced, will bear further comparison with the earlier ones of pro- 
cartilage differentiation. 
Concerning the bodies of the ribs, we have nothing to add to the descriptions 
of Giinther, Maurer (96), Osawa, and others, except as regarding the so-called 
“uncinate processes.” Giinther in his original description accords the first of these to 
the last prasternal rib, Osawa to the penultimate, but neither state their posterior 
limitations. Like those of the Ratite birds, they are apt to be easily lost in maceration ; 
but in carefully prepared specimens we have been able to trace them back, with 
* Cope, E. D.: Proc. Amer. Philos, Soc, vol. xvii. 1878, pp. 518 et seg.; and Proc. Amer. Assoc. Ady. Sci. 
1884, pt. ii. p. 474. 
* Cope, E, D.: Trans. Amer. Philos. Soc. vol. xvi. 1886, p. 249. 
