The four premolars gradually increase in size from the first to the last, but none are very large. The first premolar is a single-rooted tooth resembling that of the upper jaw; the second, third and fourth are two-rooted, like the second and third of the upper jaw, which they closely resemble in other respects.
The first molar forms the carnassial (fig. 84, V), and with the exception of the canine, is much the largest tooth of the lower jaw; it is a two-rooted tooth, with a long compressed bilobed blade, and a posterior tuberculated talon or heel. The second molar is much smaller, though likewise two-rooted, while the third molar is very small and has only a single root. All the teeth except the molars are preceded in the young animal by temporary milk teeth. These milk teeth, though smaller, are very similar to the permanent teeth by which they are ultimately replaced.
II. ENDOSKELETON.
1. The Axial skeleton.
This includes the vertebral column, the skull, and the ribs and sternum.
A. The Vertebral column.
This consists of a series of about forty vertebrae arranged in succession so that their centra form a continuous rod, and their neural arches a continuous tube, surrounding a cavity, the neural canal.
The vertebrae may be readily divided into five groups:—
1. The cervical or neck vertebrae.
2. The thoracic or chest vertebrae which bear ribs.