absence of barbules. This order contains the African ostrich, with two toes; the American ostrich (rhea), the emeu, and the cassowary, with three toes each, also the apteryx.

VIII. SAURURÆ. This order contains the single extinct bird called the archæopteryx macrura, which differed from all known birds in having had two free claws to the wing, and a long tail composed of separate vertebræ, without any ploughshare bones.

CHAPTER V.

REPTILIA: GENERAL CHARACTERS AND ORDERS.

REPTILIA (repo, I creep) have received this designation from their creeping method of locomotion, and are typically represented by serpents and snakes who actually creep. They constitute a large and important class of the vertebrata, and are extremely interesting to man, in consequence of their containing a number of venomous and formidable animals.

OSTEOLOGY.-The skull articulates with the vertebral column by means of a single condyle; each side of the lower jaw is composed of several pieces, and articulates with the skull by the intervention of the os quadratum. The number of vertebræ comprising the spinal column varies very much in the different orders. In the majority of

existing reptiles, each vertebra is procælous (pó, in front; and Koixos, hollow), i.e., concave in front, and convex behind, so that there is a perfect ball and socket-joint formed between every two contiguous vertebræ. The limbs may be absent, as in snakes, or rudimentary, as in some lizards, but generally both pair are present. Ribs are always present, but they vary greatly in form. A thin section of a reptilian bone, under the microscope, exhibits elongated oval dilatations on the plasmatic canals, best defined in the serpents, e.g., python.

absence of barbules. This order contains the African ostrich, with two toes; the American ostrich (rhea), the emeu, and the cassowary, with three toes each, also the apteryx.

VIII. SAURURÆ. This order contains the single extinct bird called the archæopteryx macrura, which differed from all known birds in having had two free claws to the wing, and a long tail composed of separate vertebræ, without any ploughshare bones.

CHAPTER V.

REPTILIA: GENERAL CHARACTERS AND ORDERS.

REPTILIA (repo, I creep) have received this designation from their creeping method of locomotion, and are typically represented by serpents and snakes who actually creep. They constitute a large and important class of the vertebrata, and are extremely interesting to man, in consequence of their containing a number of venomous and formidable animals.

OSTEOLOGY.-The skull articulates with the vertebral column by means of a single condyle; each side of the lower jaw is composed of several pieces, and articulates with the skull by the intervention of the os quadratum. The number of vertebræ comprising the spinal column varies very much in the different orders. In the majority of existing reptiles, each vertebra is procælous (pó, in front; and koíños, hollow), i.e., concave in front, and convex behind, so that there is a perfect ball and socket-joint formed between every two contiguous vertebræ. The limbs may be absent, as in snakes, or rudimentary, as in some lizards, but generally both pair are present. Ribs are always present, but they vary greatly in form. A thin section of a reptilian bone, under the microscope, exhibits elongated oval dilatations on the plasmatic canals, best defined in the serpents, e.g., python.

I. CROCODILIA.

5. Icthyopterygia (ix0ús, a fish ;
and πτερύγιον, a little wing)

6. Sauropterygia (σaúpos, and
πτερύγιον)

7. Anomodontia (ăvoμos, irregular;
and odoús, a tooth)

8. Pterosauria (TTEрóv, a wing;
and σαύρος)

9. Deinosauria (devós, frightful;
and σαύρος)

Extinct.

All the members of this order are carnivorous; they inhabit fresh water, and are found in the large rivers of both the Old and New World. They possess the following characteristic peculiarities:-The bones of the skull are firmly united together, but the sutures uniting them never become obliterated, so that the individual bones can easily be demonstrated; the two rami of the lower jaw are united in front by a suture. There is a single row of teeth implanted in distinct sockets; the base of each tooth is hollow in consequence of the absorption produced by the succeeding tooth, which is half formed, and occupies this cavity, at the base of which may be found the germ of another tooth-thus, nature has provided the means for the successive replacement, during the life of the animal, of each tooth as soon as it is worn out. The vertebral column is always completely ossified, and is divided into cervical, dorsal, lumbar, sacral, and caudal regions; the cervical vertebræ are generally nine in number, the dorsal eleven or twelve, the lumbar three or four, the sacral two, and caudal never less than thirty-five; the præsacral vertebræ are said to be always twenty-four. All the vertebræ in existing crocodilia (except the atlas, axis, two sacrals, and first caudal) are procælous. The cervical vertebræ have small ribs attached to them, and for this reason these animals have much difficulty in turning their necks. The