250 



EEPTILIA 



CLASS III 



Fig. 355. 



impressions of the membrane exhibit a number of longitudinal wrinkles or 



folds, and also numerous fine parallel striae, 

 but are otherwise smooth. 



In the pelvic arch (Figs. 355, 356) the 

 ilium is low and extended antero-posteriorly 

 on either side of the imperforate acetabulum 

 as in Dinosaurs, the pre-acetabular portion 

 being much longer than the post-acetabular. 

 Its anterior extremity is sometimes ex- 

 panded (Bhamphorhynchus), in other cases 

 slender and tapering (Pterodactylus). The 

 ischium usually fuses with the ilium, and 



Pterodactylus antiquus, Somm. sp. Upper J m ' 



Jura : Bavaria. Right lateral aspect of pelvis, excludes the pubis irom the acetabulum; 

 n, Acetabulum, below which is obturator . . , , , , . ^^ , 



foramen ; u, iiium; is, ischium; pu, Pubis. it is a much-expanded bone, pierced in most 



cases by a small perforation. The pubis 

 appears to have been very loosely attached to the anteroinferior portion of 

 the ischium, and almost invariably occurs dis- 

 placed. Some authors regard this bone as a 

 pre -pubis, and interpret the posterior ventral (i 

 element as a fused ischio-pubis. In Pterodactylus 

 the bone here called the pubis is much expanded 

 distally, and was probably united with its fellow 

 in a cartilaginous symphysis. But in Bhampho- 

 rhynchus, Pteranodon, and Nyctodactylus, it is 

 narrow and band-like, extending forwards for a 

 certain distance, and then bent inwards approxi- 

 mately at right angles so as to meet its fellow 

 of the opposite side, with which it becomes fused 

 in a ventral symphysis. 



The femur is rather longer and more slender 

 than the humerus in some forms, but in others 

 is very much shorter, as in birds ; and as in birds 

 also, it is exceeded in length by the tibia, which 

 is stout and straight. The fibula is reduced to 

 a mere splint, often fused with the tibia, and its 

 pointed distal end extending scarcely half-way 

 down the shaft of the tibia, or it may be absent 

 altogether. There are two proximal tarsals 

 (astragalus and calcaneum), which in the Bhampho- 

 rhynchidae and Ornithocheiridae are always fused 

 with the tibia. At least two distal tarsals are 

 always present. 



The hind foot is characteristically reptilian 

 in structure. The four inner metatarsals are 

 about equally developed, and bear clawed 

 phalanges, having the formula 2, 3, 4, 5, or some- 

 times, when the first two digits are clawless, the Upper' ju 

 formula is 1, 2, 4, 5. The fifth digit is almost ^T^bia™ 

 always shorter than the rest, its metatarsal 

 reduced to a mere stump, sometimes without phalanges, and sometimes with 



Fig. 356. 



Rhamphorhynchus gemmingi, v. Meyer, 

 ra ; Eichstiidt, Bavaria. i/i- 

 um ; is, Ischium ; pu, 



