492 BRITISH FOSSIL REPTILES. 



put aside the ' post-coracoid lateral eniarginations,' 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 Bimorphodon may 

 have presented, we have yet to learn. 



In all cases in which it has been observed, the sternum in Pterosauria (fig. 1) resem- 

 bles in essential characters that of CrocodUia (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 (5l),^ and having the posterior expansion (eo), which remains cartilaginous 

 in the CrocodUia, 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- 

 phodon ; 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 Pterosauria, 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 CrocodUia andi some LacerfiaJ' The restoration of the 

 bony cage of the thoracic-abdominal cavity of Pimorp/iodon (PI. 17) is based on the 

 analogy of better preserved specimens of Pterosauria 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 Bimorphodon 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. 8, fig. 26), the vertebrae lost length at this confluent tract, there 

 might be five or six sacrals articulating with the iliac bones in Bimorphodon. Von 

 Meyer figures 5 — G anchylosed sacral vertebrae in his Pterodactjjlus dubius i^ and the 

 sacrum appears to consist of at least six confluent vertebrae in Pliamphorhynchus grandi- 

 pelvis, Von Meyer.* 



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



' PI. 12, figs. 7—12. 



'-' As ill Hatteiiit, see Giiiither's excellent Memor, in ' PIpIo.s. Trans.,' Part II, 18G7, p. 13, pi. if, 

 r.gs. 17,24. 



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

 ■' Op. cit., p. 53, pi. viii, fig. 1. 



