226 REPTILIA. 



seem to possess only one large proximal, one large distal, and 

 one smaller lateral element. The first digit of the manus is 

 rudimentary or absent ; nos. II to iv are short, and bear large 

 claws ; while no. v is enormously elongated, and bent back- 

 wards to support the wing-membrane. In the pelvis, the ilium 

 is extended both forwards and backwards, and fused with the 

 much-expanded ischium, which is pierced by a small perforation; 

 the acetabulum is closed, and the pubis is excluded from it. 

 The relationships of the latter element are not quite clear, and 

 it has been regarded as a prepubis, the other large inferior 

 element being then interpreted as fused ischium and pubis. 

 The femur is slender and shorter than the tibia ; the fibula is 

 incomplete, a mere pointed style, often fused with the tibia ; 

 the astragalus and calcaneum are distinguishable, the former 

 sometimes fused with the tibia : and of the five digits in the 

 pes four bear claws. No dermal armour has been observed, 

 but there are abdominal ribs in the ventral wall of the body- 

 cavity. The smooth wing-membrane has been observed in 

 impression on the Bavarian Lithographic Stone, and one 

 specimen (fig. 139) proves that it extended beyond the hind legs 

 to the basal portion of the tail ; the long tail of the same 

 specimen exhibits a rhomboidal flap of membrane at the distal 

 extremity. 



Dimorphodon (fig. 138). The oldest known genus, Dimorphodon, is 

 represented by nearly complete skeletons. The skull is of relatively 

 enormous size, deepened in form, and of extreme lightness ; the brain- 

 case is unusually small. The large narial opening on each side is 

 separated from the orbit by an equally large or larger autorbital 

 vacuity. The long axis of the quadrate bone is vertical. The jaws are 

 toothed to the extremity ; there being large, irregularly spaced teeth in 

 front, very small and more closely arranged teeth behind. The number 

 of the presacral vertebrae is unknown, but one of them seems to be 

 lumbar (destitute of ribs), and there are probably four in the sacrum ; 

 the caudal vertebra} are at least 30 in number, much elongated, and 

 some with chevron bones. The tail is stiffened by ossified tendons. 

 The ribs increase in length to the fifth or sixth, and seem to exhibit traces 

 of epipleural cartilages. The pectoral arch is imperfectly known, but the 

 scapula and coracoid are clearly fused together. In the manus the first 

 digit is represented merely by a styliform bone ; nos. n to iv are clawed 

 and exhibit the phalangeal formula 2, 3, 4 ; no. v, or the wing-digit, has a 



