ICHTHYOSAURIA 115 



teeth were inserted, not in separate sockets, as are those of the 

 crocodiles and many other reptiles, but in long, deep grooves, and 

 were easily lost, indeed so easily lost that one late American form 

 was originally described as edentulous, and it was not till a number 

 of years had elapsed that the teeth were found. The nostrils 

 were small, and situated far back on the sides of the face, near the 

 eyes. The eyes were very large, not only in proportion to the size 

 of the skull, but, in the largest species, actually attaining in some, 

 perhaps, the size of a human head. The eyeball was surrounded 

 in front by an extraordinarily large and strong ring of ossifications 

 in the sclerotic membrane, giving not only protection to the eye 

 under the varying pressure of the water, but also greater control over 

 vision. The neck was very short, so short, in fact, that no con- 

 struction was visible in the living animal between the head and 

 body; it was capable of only slight movement. The trunk was 

 elongated and relatively slender, sometimes with more than fifty 

 vertebrae in it. The tail also was long and flattened, ending in all 

 the later species in a large fleshy fin, resembling the caudal fin of 

 many fishes in shape and doubtless also in function. There was 

 also a large dorsal fin, supported by hardened or calcified sinews, 

 in shape like the dorsal fin of most fishes and many cetaceans. This 

 character is absolutely unique among reptiles, so far as is known, 

 and was one of the extreme specializations of water life. The hind 

 limbs were smaller, often much smaller than the fore ones, and both 

 were quite fin-like in life, or rather flipper-like, though not at all 

 fin-like in structure. The skin was smooth and bare. In brief, 

 to quote Fraas's words: 



The general aspect of the ichthyosaurs was very dolphin-like. The body 

 was everywhere naked and probably dark in color. The head was produced 

 in front into a long, slender snout, and was closely joined to the body posteriorly 

 without indications of a neck. The body itself was cylindrical, expanded 

 in front by the large thorax and abdomen, but rapidly diminishing into the 

 long, slender, and strong tail. Close behind the head were the front paddles, 

 which in some species were broad and shovel-like, in others elongated and 

 pointed. The hind paddles were smaller than the front ones, sometimes greatly 

 reduced in size, their function replaced by that of the very broad tail. 



From the foregoing descriptions and the restoration shown 

 in Fig. 51, we see how very fish-like, or rather dolphin-like, these 



