250 



EEPTILIA 



CLASS III 



Pig. 355. 



Pterodaotylus antiquus, Somm. sp. Upper 

 Jura ; Bavaria. Right lateral aspect of pelvis. 

 a, Acetabulum, below which is obturator 

 foramen ; il, Ilium ; is, Ischium ; pit, Pubis. 



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 (Bhamphorhi/nchus), in other cases 

 slender and tapering (Pterodactylus). The 

 ischium usually fuses with the ilium, and 

 excludes the pubis from the acetabulum ; 

 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 antero-inferior portion of 



the ischium, and almost invariably occurs dis- 

 placed. Some authors regard this bone as a 



pre -pubis, and interpret the posterior ventral 



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 BJmmpho- 



rhynchus, Pteranodon, and Nyctodactylm, 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), Avhich in the Bhampho- 



rhyiichidae 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- „, ^ , , . . ,, 



^ . 1 1 ^ T • 1 1 1 Rhamphorhynchus gemmingt, v. Meyer, 



times, when the nrst two digits are Clawless, the Upper Jura; Elchstadt, Bavaria. Vl- 

 £ T • 1 .-> ^ K rpi iij-ii. J- "j. • 1 J. /i Femur; il. Ilium; is, Ischium; pv, 



formula IS 1, 2, 4, 5. ihe fifth digit is almost pubis ; f, Tibia. 



always shoi'ter than the rest, its metatarsal 



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



Fig. 356. 



