70 



FOSSIL REPTILIA OF THE 



truth of the matter can put aside the ' post-coracoid lateral emarginations,' and other 

 modifications defined in that Monograph as ' distinctive Pterosaurian characters/ No 

 Bird has shown any approach to them. What modifications of the Pterosaurian sternum 

 Dimorpliodo7i may have presented, vi^e have yet to learn. 



In all cases in vi'hich it has been observed, the sternum in Fterosauria (fig. 1) resem- 

 bles in essential characters that of Crocodilia (fig. 2); its chief part is a longitudinal, com- 

 pressed, deep bar (59), expanding laterally, some way from the fore-end, for the articulation 

 of the coracoids (51),^ and having the posterior expansion (eo), which remains cartilaginous 

 in the Crocodilia, more or less ossified, in the form of a thin semicircular plate : but the 

 whole bone, though adaptively modified for attachment of muscles of flight, preserves the 

 characteristic shortness compared with the trunk, and offers a striking contrast to the long 

 and large subabdominal plastron in most birds of flight. There is no distinct T-shaped 

 episternum, such as exists in most Lacertia, and no trace of clavicles as in Lizards and 

 Birds. Distinct lateral elements for articulation with sternal ribs I have not satisfactorily 

 made out in any specimen. 



The abdominal haemal arches consist of slender haemapophyses and of chevron-shaped 

 haemal spines. 



There is evidence of one lumbar or ribless vertebra anterior to the sacrum, in Dimor- 

 pliodon ; and no Pterosaurian appears to have shown more than two such vertebras : in this 

 character we are again directed to the true Reptilian relation of Fterosauria, and 'warned 

 off the beguiling marks of Avian affinity. 



The indications of epipleural appendages of ribs, more or less bony, if rightly inter- 

 preted, answer to the gristly ones in Crocodilia and some Lacertia?' The restoration of the 

 bony cage of the thoracic-abdominal cavity of Dimorphodon (PI. XX) is based on the 

 analogy of better preserved specimens of Fterosauria in regard to this part of the skeleton. 

 Scattered elements of the haemal arches, ' abdominal ribs,' &c., have alone been met with 

 in the specimens of DimorpJiodon hitherto obtained. 



The sacrum, on the probable hypothesis of retention of the length of centrum shown 

 in the lumbar vertebra, would include at least four vertebras ; if, as by the analogy of the 

 sacrum (figured in PI. II, fig. 26, of the Monograph, &c., Supplement No. 1, 1859), the 

 vertebrae lost length at this confluent tract, there might be five or six sacrals articulating 

 w^ith the iliac bones m DimorpJiodon. Von Meyer figures 5 — 6 anchylosed sacral vertebrae 

 in his Fterodactylus duhius and the sacrum appears to consist of at least six confluent 

 vertebrae in Rhampliorhynclms grandipelvis, Von Meyer.* 



With all the evidence that the Pterosauria, like the Binosauria and Bicynodontia, 



' 'Monograph on Cretaceous Reptilia,' Supplement, No. Ill (1860), PI. II, figs. 7 — 12. 

 2 As in Hatteria, see Giinther's excellent Memoir, in ' Philos. Trans.,' Part II, 1867, p. 13, pi. ii, 

 figs. 17, 24. 



2 Op. cit., p. 17, pi. vi, fig. 1. 

 * Op. cit., p. 53, pi. viii, fig. I. 



