274 The Teeth of Fishes. [Sess. 
Ophidian Reptiles—true serpents, the ribs being the means 
of locomotion. There are two groups—non-poisonous and 
poisonous. (1) Non-poisonous Snakes. These have one row 
of teeth in the lower and two in the upper jaw. In the upper 
they are distributed on the jaw bone, palatine and pterygoid 
bones. The teeth are recurved, and are anchylosed to the 
bone. The teeth during their development have a horizontal 
instead of a vertical position, and are thus protected from 
displacement, as happens in other creatures. They have no 
canals in their teeth for ejecting poisonous saliva. (2) Poison 
Snakes—Puff-adders, rattlesnake, vipers, &c. The maxillary 
bone carries no teeth behind the poison-fang. This is a 
splendid example of the doctrine of adaptive modification, 
where in the course of generations the other teeth which we 
see in the non-poisonous snakes have disappeared by the 
development of the poison-fang. 
Crocodilia. In this order the teeth are implanted in 
sockets: they are conical and sharp, while one or two are 
larger than the others. 
Birds. In the present age birds have no teeth, but from ~ 
excavations in different parts of the world fossil remains have 
been discovered proving that some of the birds of the past — 
were possessed of true teeth. 
We now come to the mammals, and, as far as can be © 
gathered from fossil remains, the typical dental formula — 
was— 
wee an aes ae 4. 3 
incisors 3; canines +; premolars +; molars 3 
Edentata—sloths, armadillos, and ant-eaters. In these the 
teeth are of simple form, grow from persistent pulps, and do 
not differ much from one another in appearance. Most of 
them have no incisor teeth. 
In Cetacea we have two groups—toothed whales or Odonto- — 
ceti, and the whalebone whales or Mysticoceti. The dolphin 
has very numerous slender teeth, which interdigitate with one 
another. They are fastened on cartilage, and could be pulled 
out en masse. The pilot whale or Grindhval of the Faroe 
islanders, which attains a length of twenty feet, is often 
caught in the North of Scotland. The teeth are fewer than 
in the dolphin, and have an edge-to-edge bite. In the sperm 
whale the teeth are numerous in the lower jaw, but are stunted ~ 
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