160 PICTURESQUE SKETCHES 



twenty-five to thirty vertebrae (fig. 58), which, like 

 those of the neck, present to each other nearly flat 

 surfaces ; and the tail, which was of moderate length 

 but very powerful, had an additional twenty-five, also 

 flattened in a similar way. All the vertebrae had 

 strong and large processes or projecting plates of 

 bone for the attachment of muscles (see fig. 58). 



The trunk and extremities of this singular animal 

 present many points of interest, especially with re- 

 gard to contrivances introduced to meet the wants of 

 a marine reptilian animal. 



The ribs of vertebrate animals are, properly speak- 

 ing, appendages to the vertebrae, one pair being usual- 

 ly developed from each vertebra, to approach or meet 

 on the under side of the animal. The Plesiosaurus, 

 however, was provided with sets of bones, each set 

 consisting of seven, which connected these free ex- 

 tremities, rendering them very strong, but also al- 

 lowing a considerable amount of play, since the 

 connecting bones could slide upon one another. This 

 contrivance admitted of much greater expansion of 

 the lungs than is common in reptiles. 



The portion of the body corresponding to the 

 breast-bone, and connecting the fore extremities with 

 the vertebral column, is strong but not complicated, 

 and appears better adapted for allowing free mo- 

 tion in the paddles, and so propelling the animal 

 through the water, than for supporting the weight of 

 the body on land. Nearly the same may be said 

 of the pelvis, which supports the hind extremity, 

 and which exhibits about a corresponding degree 

 of strength. There is also a beautiful contrivance 

 enabling the animal to make use of its extremities 



