J. W. HTTLKE ON THE VERTEBILE OF ORNITHOPSIS. 35 



EXPLANATION OF PLATES III. & IV. 



AU the figures are about one fourth the natural size."' 



Fig. 1. Side view of cervical vertebra. (No. II. 4, Mr. Fox's Catal.) (The 

 prsezygapophyses, the dia- and parapophysis and a piece of the 

 border of the posterior articular cup have been broken ofi",) 



Fig. 2, Under surface of another cervical vertebra. (No. II. 6, Mr. Fox's 

 Catal.) 



Fig. 3. Front view of another cervical vertebra. It is somewhat distorted by 

 pressure, and the left praszygapophysis, dia- and parapophysis have 

 been broken ofi". (No. II. 3, ]\Ii'. Fox's Catal.) 



Fig. 4. Side view of the same (postzygapophysis broken off). 



Fig. 5. Front view of trunk- vertebra. 



Fig. 6. Side view of trunk-vertebra. (The free extremity of the diapophysis is 

 detached.) 



Fig. 7. Back view of trunk- vertebra. (No. II. 1, Mr. Fox's Catal.). 



In all the figures the letters have the following signification : — 



'j^rz, praezygapophysis. c, cup. 



'psz, postzygapophysis. s.c, side chamber. 



za, zygantrum. n.cl, neural canal. 



Z8, zyposphene. n.cr, neural crest. 



^, parapophysis. ^t, side pit. 



d, diapophysis. r, riblet. 

 6, ball. 



Discussion-. 



Prof. Seelet supported the view of the pneumatic character of 

 the vertebral cavities in this genus by reference to the Chelonians 

 and Birds, and believed that the tissue of the dorsal vertebrae had 

 been excavated and absorbed owing to the pressure of an air-sac upon 

 the vertebrae, due to a sacculate condition of the lungs. He pointed 

 out the value of the new evidence obtained with regard to the 

 neural arch ; and (if we may accept the evidence of the American 

 genera as to the carpus and tarsals) we seem to have proofs in these 

 animals of the existence of a suborder of Dinosaurs in which peculiar 

 skeletal modifilcations are associated with a pneumatic skeleton. 



Dr. Meryon took exception to the explanation given by Prof. 

 Seeley as to the absorption of portions of the vertebrae. He sug- 

 gested that the analogies were with the Sharks and Eays rather than 

 with Birds. 



Mr. Htjlke replied to Dr. Meryon that while the cervical vertebrae 

 indicate great mobility, the dorsal vertebrae are very JGLrmly locked 

 together. Against the view that the parallel of the singular cham- 

 bered structure was to be found in the Sharks and Eays, he pointed 

 out that this structure is, in Ornithoj)sis, confined to the dorsal 

 region, and does not extend through the whole length of the ver- 

 tebral column, as is the case with cartilaginous fishes. 



d2 



