It has been already remarked, that the large Cartilaginei would not pass correctly into the others, and obviously seem to claim the highest post. At some later period the principle may probably be discovered whereupon their union with the higher Osseous fishes depends. Both are at all events Abdominales.
Eleventh Class.
Myozoa, Rhinozoa—Reptilia.
3542. Body entirely naked or covered with scales, with distinctly separate and red-coloured muscles; two nostrils permeable throughout.
As the Muscular system is here the characteristic organ, it must be regarded principally in the division of the present class; the limbs also exhibit nowhere so great a variety as in this class, since they are in some cases wanting, while in others two only, in some four, are present. In place of fin-rays true toes have, however, made their appearance, these again indicating the greatest variety in the number of the joints; but meanwhile there are in no instance more than five toes.
The osseous system is constructed after the pattern of that of the Thricozoa, and is never furnished with dorsal rays as in Fishes.
The dental formula begins also to be regular. The teeth stand usually in the superior intermaxillary bone, and are sometimes pointed, at others obtuse; in the Ichthyosauri and Crocodiles they are even inserted by gomphosis, as in the Thricozoa. In many Serpents additional kinds of teeth occur, namely, the curved poison-teeth or fangs, which have an involuted groove traversing their concavity. In most Reptiles teeth also occur upon the palatal, but there are no longer any upon the lingual bone. In the Chelonia or Tortoises the teeth are entirely wanting, and they are also scarcely indicated in the Asquamous Salamanders and Frogs.
The os quadratum is found as in Birds; in Serpents, however, the mastoid bone has been freed, and hence the capability possessed by these creatures of expanding the mouth.
Viewed in accordance with the perfection of the limbs, the Salamanders and Frogs ought to be regarded as the highest in rank; but their scaleless tegument, their development out of spawn in the water, as well as branchiæ brings them near to the Fishes. In other respects their position is determined by the dental formula, which, as I have already shown, belongs to the limbs and thus to the motor system.
The position of the nostrils is now, throughout the class, in front of and upon the snout, being no longer situated almost on the forehead or vertex, as in Fishes. Their relation to the scales is likewise of importance for the purposes of division.