86 
FOSSIL REPTILIA OF THE 
case upon a Reptilian, in the other upon a Mammalian type, and both show analogies to 
the Vertebrates which the waters first brought forth,” But that the Ichthyopterygians 
did not breathe by means of gills is shown by the absence of the branchial framework, 
and by the presence, position, and structure of passages leading from the nostrils to the 
palate for the course of currents of air on their way to lungs, which were protected and 
worked by movable thoracic-abdominal costal girdles, tierein these old Sea-reptiles rise 
higher in structure than some modern cold-blooded air-breathers such, e.g. as Batrachians 
and Chelonians. 
An Ichthyosaur by the shortness, one may say absence, of neck, and equality of 
width of the back of the head with the front of the chest, shares with the IVhale a 
resemblance to Fishes, but pushes the likeness closer in the greater number and less 
length of the vertebrae, and in the indication of the main joints of the backbone being- 
elastic bags filled with fluid, occupying the intervertebral spaces of the biconcave 
centrums, as in Fishes, Labyrinthodonts, and modern perennibranchiate Batrachians. 
Being cold-blooded, and with a small brain needing a much less supply of oxygen for 
its work, the Ichthyopterygians, like Fishes, had this advantage over Whales, that their 
stern-propeller could have the form best adapted for a swift straightforward course 
through the water.^ The horizontality of the tail-fin of the Whale tribe relates to their 
need, as large-brained, warm-blooded air-breathers, to have easy and speedy access to 
atmospheric air. Without the means of displacing a mass of water in the vertical 
direction by such broad tail-fin the head of the Whale could not be brought with the needed 
rapidity to the surface for the purpose of breathing. Nevertheless the Cetaceans are 
restricted to their element as closely as Fishes, and perish almost, if not quite, as soon 
when cast ashore, whilst the Ichthyosaurs were less limited in regard to medium, and had 
a power upon dry land which neither of the other aquatic vertebrates enjoy. 
That our Sea-lizards occasionally sought the shore is to be inferred from the strong 
inverted osseous arch supporting their fore fins, spanning across the chest from one 
shoulder-joint to the other. In structure this arch closely resembles that in a group of 
aquatic Mammals {Ornithorhgnchus), which similarly surpass Cetacea in having a 
command of both land and water, although, by their low position in the mammalian 
class, they have closer alliance to the Eeptilia. 
There is reason to infer, from examples of diminutive Ichthyosaurs fossilized within the 
abdominal cage of larger ones, and with the snout directed toward, or partly protruding 
from, the pelvic outlet, that they were ovo- viviparous and, as a rule, uniparous, reptiles.^ 
Others may have sought the shore for sleep or copulation, and have been enabled, by reaction 
^ “ Note on the Dislocation of the Tail at a certain point ohservable in the Skeleton of many 
Ichthyosauri,” ‘Trans, of the Geological Society,’ 2nd series, vol. v, 1838, p. 51 1, pi. xlii. 
2 As first shown in the specimen of Ichthyosauri from the Lias of Boll, described and figured by 
G-eorge Friedrich Jager, op. cit., tab. i, fig. 4 ; subsequently noted by Quenstedt in specimens in 
the Tubingen Museum; also by Channing Pearce (‘ Report of the British Association,’ 1874). 
