608 E. B. BRANSON 



literature on the subject, having examined very few specimens of the 

 vertebrae themselves. He says: "The neural arches of the tail 

 and thorax rest exclusively upon the posterior disk (pleurocentra of 

 Cope)." 1 As already shown in the present article, the neural arches 

 are gradually shifted on to the intercentra in the posterior part of the 

 thoracic region, and in the caudals the intercentra furnish the greater 

 part of the support. Dr. Gadow's figures 2 of two vertebrae in the 

 British Museum shows that the neural arches rest against the inter- 

 centra in the dorsal region. Cope's figures 3 of the anterior caudals 

 show that the intercentra form most of the support for the arches. 

 (See Fig. 16.) 



Dr. Gadow says: 



In the thoracic vertebrae the diapophyses of the neural arches alone carry 

 the single-headed ribs. In the cervicals the articular facet extends downward 

 and forms a shallow groove on the caudal portion of the intercentrum. 4 



In all of the thoracic vertebrae the rib is borne by both the arch and 

 the intercentrum. The intercentra of the atlas and axis are the only 

 ones anterior to the caudals that have no facet for rib articulation. 

 The size of the rib facet on the intercentrum increases gradually 

 posteriorly, and on the sacral vertebrae it is more than 2 cm in diameter. 

 Furthermore the ribs are not all single-headed. As Cope has pointed 

 out, 5 the sacral ribs are distinctly double-headed, though the capitulum 

 and tuberculum are not widely separated. Five or six of the ribs 

 just anterior to the sacrum have the capitulum and tuberculum 

 separate, though not as distinctly as in the sacrals; and anterior to 

 these the ribs are really double-headed, for they articulate with both 

 the diapophysis and intercentrum. 

 Dr. Gadow says of the pleurocentra: 



They are, moreover, the pieces which, in Eryops, are attached to the caudal 

 end of the cervical vertebrae, figured by Cope, and there actually and rightly 

 called hypocentra pleuralia. 6 



1 Loc. tit., infra, p. 21. 



2 Philosophical Transactions of the Royal Society of London, Vol. CLXXXVII, 

 p. 41, Fig. 41. 



3 Transactions of the American Philosophical Society, Vol. XVI, Plate 1, Fig. 1. 



4 Loc. cit., pp. 21. 22. 5 Palaeontological Bulletin, No. 32, p. 15. 

 6 Loc. cit., p. 22. 



