LIASSIC FORMATIONS. 



69 



in the specimen fignrcd in PI. XVIII. Their articulations witli the vertebrae have already 

 been noticed. The ribs increase in length to the fifth or sixth, with some dimijuition of 

 breadth after the third, and acquire a characteristic tenuity beyond the sixth pair. On 

 the outer surface a groove extends from the neck, or interspace between the head and 

 tubercle downward ; the front border of the groove being somewhat prominent, but sub- 

 siding in the hinder ril)s, Epipleural appendages are indicated in some specimens ; 

 but the indications are feeble, and, if rightly so interpreted, these appendages seem to 

 have been but partially ossified. 



The sternal ribs, beyond the sternum, unite below with the free ends of the abdominal 

 V-shaped, intermuscular styles. 



The irregular elongate mass (marked 18 in pi. xxviii of Buckland's Memoir) and 

 conjectured to be "sternum — nnich broken, and its form indistinct " (loc. cit., p. 221) in- 

 cludes two crushed cervical vertebra?, and part of a third. Of the sternum I have not been 

 able to discern a satisfactory trace in any of the specimens of Bimorphodon ; its propor- 

 tions and position are, therefore, indicated in the ' restoration' (PI. XX) according to the 

 analogy of that in Pterodactylus suevicus} Pt. simus," and in Tthamphorhynchm? 



In the main, as regards breadth of the hind part and depth of the fore part, the breast- 

 bone of Ptei'osauria is formed on the Ornithic pattern ; i. e. it is shield-shaped, and it 

 has a keel. Put the keel does not descend from the expanded portion ; it is formed, as 

 shown "in a former Monograph (Suppl. No. Ill, p. 8), by the vertical development of the 

 anterior production answering to the ossified sternum of Crocodiles and to the episternum 

 of Lizards. I would recommend a comparison of the figures of the sternum in Iguana and 

 Notornis, given at p. 21, vol. iii, of my ' Anatomy of Vertebrates,' to whosoever may 

 desire to form an opinion of the evidence of affinity to Birds or to Reptiles, respectively, 



afforded by the Pterosaurian sternum, especially as this is illustrated in figures 7 to 12 of 

 PI. II of tlic Supplement No. Ill, above cited. No one desirous of simply getting at the 



• Quenstedt, loc. cit. (18.")5). 



' 'Monograph,' Suppl., No. Ill (18G0), PI. II, figs. 7—12. 



^ Von Meyer, op. cit. (18G0), pi. vii, figs. 1 and 3, and pi. i.\, fig. I. 



Fig. 1. 



Fig. 2. 



