LIASSIC FORMATIONS. 
69 
in the specimen figured in PI. XVIII. Their articulations with the vertebrae have already 
been noticed. The ribs increase in length to the fifth or sixth, with some diminution 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 ribs. 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 1 8 An pi. xxviii of Buckland’s Memoir) and 
conjectured to be “ sternum — much broken, and its form indistinct ” (loc. cit., p. 221) in- 
cludes two crushed cervical vertebrae, 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. smus,^ and in Phampliorhynchus? 
In the main, as regards breadth of the hind part and depth of the fore part, the breast- 
bone of Pterosauria is formed on the Ornithic pattern ; i. e. it is shield-shaped, and it 
has a keel. But 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. hi, of my ‘Anatomy of Vertebrates,’ to whosoever may 
desire to form an opinion of the evidence of affinity to Birds or to Reptiles, respectively. 
Fig. 1. ''' Fig. 2. 
afforded by the Pterosaurian sternum, especially as this is illustrated in figures 7 to 12 of 
PI. II of the Supplement No. Ill, above cited. No one desirous of simply getting at the 
^ Quenstedt, loc. cit. (1855). 
* ‘Monograph,’ Suppl., No. Ill (1860), PI. II, figs. 7 — 12. 
3 Vnn Meyer, op. cit. (1860), pi. vii, figs. 1 and 3, and pi. ix, fig. 1. 
