56 REPOur— 1839. 



it consists of a short mesial process, and two broad lateral ex- 

 pansions. 



A strong triradiate bone, which seems to represent, as in the 

 Chelo7iia, the scapula and clavicle united, arches from the outer 

 extremity of the ento-sternal branch to the corresponding ex- 

 tremity of the coracoids, with which it combines to form the 

 shoulder-joint, and near which point it sends upwards and 

 obliquely backwards a branch or process representing the true 

 scapula. 



Pectoral extremity . — The humerus is a stout and moderately 

 long bone, rounded at its proximal extremity, and flattened as it 

 approaches the elbow-joint : it is curved slightly backwards. 



The radius and ulna are both short and flat bones, but rela- 

 tively longer and more distinctly marked than in the Ichthyo- 

 sauri : the radius or anterior of the two bones is nearly straight ; 

 the ulna is curved, with its concavity directed towards the radius. 



The carpus is very distinctly defined, consisting of a double 

 row of small flat rounded ossicles, from six to eight in number. 

 The metacarpal bones, five in number, are elongated, slender, 

 flattened, and slightly bent. The digits never exceed the num- 

 ber of the metacarpal bones, but consist generally of more than 

 the usual number of phalanges. The first, or radial one, cor- 

 responding with the thumb, has generally 3, the second 6 or 7? 

 the third 8 or 9, the fourth 8, and the fifth 6 phalanges. These 

 bones are moderately long and slender, but gradually taper to- 

 wards the distal end of the digits : they are joined together in 

 each digit by flattened surfaces, indicative of a mere yielding 

 movement on one another. There can be little doubt that they 

 were enveloped, like the paddles of the Cetacea, in a common 

 sheath of integument. From the natural curve of the digits, 

 the paddles of the Plesiosaur nmst have had a more elegant and 

 tapering form, and have possessed greater flexibility, than those 

 of the modern Cetacea. 



Pelvic arch. — The hinder or pelvic extremities almost always 

 equal, and sometimes, as in PI. macrocephalas, exceed the an- 

 terior ones in size. 



The pelvic arch consists of a short and strong ilium, and a 

 broad pubis and ischium, both of which are expanded in the 

 antero-posterior direction, analogously to the coracoids in the 

 pectoral arch. 



Pelvic extremity. — The radiated appendages of the pelvic 

 arch so closely correspond with those of the pectoral arch as to 

 require little to be said respecting them. In the modifications 

 of the two bones of the leg, tlie posterior one, or fibula, corre- 

 sponds in its curved form with the ulna, and illustrates an 



