BIRD FROM THE WEALDEN OP BROOK. 



211 



few vertebras in the sacrum ; while Ichthyornis dispar has no renal 

 recesses in the middle of the sacrum ; and the Gannet makes a 

 sufficiently near approximation to the form of the articulation to 

 remove any improbability as to its being a modified Avian form. 



I therefore venture to submit, on the evidence of the resemblances 

 and considerations which have been discussed, that Ornithodesmus 

 is probably a bird ; but it differs from existing birds, so as to suggest 

 that it is a link towards lower forms. It cannot be placed in any 

 existing division of the class, but approximates towards Dinosaurs 

 in a way of which no bird had previously given evidence. 



I am indebted to Dr. Henry Woodward, FJt.S., for facilities 

 afforded me in making this study. 



EXPLANATION OF FIGURES. 

 Plate XII. 



ns, neural spine ; t, transverse process ; z, prezygapophysis ; pz, postzygapo- 

 pbysis ; np, neural platform ; pn, pneumatic foramen ; vc, vascular groove. 



Fig. 1. Dorsal view of sacrum of Ornithodesmus cluniculus. 



2. Ventral view of sacrum. 



3. Lateral view of sacrum. 



4. Anterior articular end of first sacral vertebra. 



5. Posterior articular end of last sacral vertebra. 



6. Posterior articular face of last sacral vertebra of Aptenodytes 



Forsteri. 



(For the Discussion on this paper, see p. 219.) 



