372 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. IV. 



tooth of the Lepidosteus, an existing genus of river fishes. 

 (See " Medals of Creation," PL VI. fig. 9.). 



The nasal apertures, or openings of the nostrils, are placed 

 as in the Plesiosaurus, near the anterior angle of the orbit. 



The orbits are very large, and the sclerotic coat, or capsule 

 of the eye, has in front an annular series of bony plates, 

 which often occur in their natural position, and are beauti- 

 fully displayed in many of the specimens in the Cases before 

 us. This mechanism is not possessed by fishes, but is analogous 

 to that observable in the eyes of turtles, lizards, and many 

 birds ; as, for example, in the owl and eagle : it confers on the 

 eye additional power of adaptation, and intensity of vision. 



The vertebrae, of which there are upwards of one hundred 

 and forty in the individuals of some species, are, as we have 

 already remarked, very short in their antero-posterior dia- 

 meter (i.e. from front to back), and deeply cupped on each 

 articulating face. The annular part is not united to the 

 body of the vertebra, as in quadrupeds, nor connected by 

 suture, as in Crocodiles, but terminates on each side in a 

 compressed oval base, which fits into corresponding sockets 

 placed on the boundary line of the spinal depression on the 

 body, and thus completes the neural canal. The first and 

 second vertebrae are anchylosed together, and have additional 

 sub-vertebral, wedge-shaped bones, which render this part of 

 the column a fixed point of support. 1 



The pectoral arch presents a remarkable resemblance to 

 that of the Ornithorhynchus, or Duck-billed Platypus of New 

 Holland. The episternum is of a triradiate form ; the clavicles 

 are strong, elongated, and slightly curved ; the scapulae ate 

 stout and broad, and in the form of a parallelogram ; the 

 coracoids are of a hatchet-shape, with a strong, thick, glenoid 

 extremity, and a thin mesial expansion, which articulates 

 with the episternal bone. 2 



The pelvic arch consists of the same elements as in the 

 Plesiosaurus, but the ischium and pubis are much smaller 

 than in that genus. The ilium is a short, simple, strong, and 

 compressed bone, slightly expanding as it descends, to com- 



1 This structure was first demonstrated by Sir Philip Egerton. See 

 Geol. Trans. Second Series," Vol. V. p. 187, PI. XIV. 



2 See Dr. Buckland's " Bridgewater Essay," PI. XII. 



