Birds are in some ways the highest of the vertebrate animals. They represent the climax of that passage from water to land which the backboned series illustrates. Their skeleton is more modified from the general type than that of mammals; their arrangements for locomotion, breathing, and nutrition are certainly not less perfect; their body temperature, higher than that of any other animals, is an index to the intense activity of their general life; their habitual and adaptive intelligence is familiarly great, while in range of emotion and sense impressions they must be allowed the palm. It is, in fact, only when we emphasize the development of the nervous system, and the closeness of connection between mother and offspring, that the mammals are seen to have a right to their pre-eminence over birds. Birds and mammals represent two divergent lines of progress, and stand in no close connection, but the affinities between birds and reptiles are sufficiently marked to warrant their being included in a common class (Sauropsida), in contrast to the amphibians and fishes (Ichthyopsida) on the one hand, and Mammalia on the other. Among the numerous points of difference which separate birds from their nearest relations, the reptiles, and from mammals, the following may be noticed: ------------------------+-----------------------+------------------+ | REPTILES | BIRDS | Covering | Scales or scutes | Feathers | Number of fingers | Always more than three| At most three | ” ” skull condyles| One | One | Number of aortic arches | At least two | One, right | Diaphragm | Only incipient | Only incipient | Blood | Cold | Hottest | Position of optic lobes | On top of brain | At sides of brain| Parturition | Ovi- or viviparous | Oviparous | ------------------------+-----------------------+------------------+ ------------------------+---------------------- | MAMMALS Covering | Hair Number of fingers | Five or fewer ” ” skull condyles| Two Number of aortic arches | One, left Diaphragm | Complete Blood | Warm Position of optic lobes | Covered up Parturition | Except two viviparous ------------------------+---------------------- But those contrasts are only a few of the less technical selected from Professor Huxley’s masterly comparison of the three classes. To appreciate the full extent of the resemblances and differences between birds and reptiles, and the contrast between both and mammals, the reader must consult Huxley’s _Anatomy of Vertebrate Animals_.