﻿LIASSIC FORMATIONS. 



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The distal breadth of the femur is 4 inches 8 lines ; the non-articular surface is smooth, 

 except near the two ends, where there are rough, longitudinal ridges and depressions, 

 indicative of ligamentous insertions. 



Both tibia (Tab. IX, C6) and fibula (ib., 67) are broader in proportion to their length 

 than their homotypes in the fore limb. The posterior distal angle of the fibula is more 

 decidedly truncate, for articulation with the middle tarsal, than is the corresponding 

 part of the ulna. The inter-osseous space is a long ellipse with pointed ends, about 

 an inch in width across the broadest part. 



The tarsus (Tab. IX, 68), like the carpus (ib., 56), consists of six bones, in two rows 

 of three each. The tibial bone of the first row is broader, in proportion to its length, 

 than its homotype in the carpus ; and this is the proportional character of all the bones 

 of the tarsus, save that which intervenes between the fibula (67) and the fifth digit (69), 

 the metatarsal of which passes outside the distal tarsal series. 



The metatarsal of the innermost tibial, or first digit, is 1 inch 4 lines in length, 

 10 lines in breadth, and supports three phalanges; the total length of the digit, 

 including the metatarsal, is 4 inches 8 lines. The metatarsal of the second digit is 

 1 inch 9 lines in length, and supports six phalanges, the last being 4 lines in length ; 

 the total length of this digit, including the metatarsal, is 8 inches 6 lines. The meta- 

 tarsal of the mid-digit is 2 inches in length, and supports nine phalanges ; the total 

 length of this digit, including the metatarsal, is 1 foot. The metatarsal of the fourth 

 digit is 1 inch 11 lines long; the fibular side of its base is more produced than in the 

 others ; it supports a digit of eight phalanges, and this, including the metatarsal, is 

 I foot 1 inch in length ; the metatarsal of the fifth digit is 1 inch 10 lines in length, and 

 supports six phalanges, the last of which is broader and flatter than in the other digits ; 

 the total length of the fifth digit, including the metatarsal, is 10 inches 2 lines. The 

 breadth of the leg is 5 inches 5 lines ; the length of the tibia 3 inches ; that of the 

 fibula 2 inches 9 lines. The breadth of the metatarsus is 4 inches 7 lines. The total 

 length of the hind limb is 2 feet A\ inches. The hind limb, though longer and larger 

 than the fore limb, repeats the character of relative shortness in proportion to the 

 trunk, as engraved with the same parts in Plesiosaurus homalospondi/Ius. The neural 

 spines of the trunk are shorter, with wider intervals, exemplifying the superior vigour 

 and locomotive power of the longer-necked and larger-finned species (Tab. VIII.) 



We see in PL rostratus a correlation of the size of the head with that of the 

 anterior laniary teeth, and with the shortness of the neck. But the head is pro- 

 portionally less compared with the trunk, and the neck is shorter, and has fewer 

 vertebrae, than in the PL macrocephalus* These characters, with the greater lengthening 

 and attenuation of the muzzle in PL rostratus, indicate a nearer step in affinity toward 

 the Teleosaurian marine reptiles. 



* ' Geological Transactions,' 2nd series, vol. v, pi. sliii. 



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