They may be " rootless " masses brought upon the top of the later beds by thrustplanes.
The premolars and molars may be rooted or rootless, with tuberculated or laminated crowns, and are arranged in an unbroken series.
- Vertical and Longitudinal Section through the Skull of the Beaver (Castor fiber), showing the brain-cavity, the greatly developed plates of bone in the nose-cavity, the mode of implantation of the ever-growing chisel-edged incisor, and the curved rootless cheek-teeth.
Rootless, and either cusped or formed of parallel plates, this diversityof structure often occurring in the same family.
Sewellels are medium-sized terrestrial rodents, with no postorbital process to the skull, which is depressed in form, and rootless cheek-teeth, among which the premolars number I, the first in the upper jaw being very small.
The second section, Castoroidea, of the present group includes only the family Castoridae, represented by the beavers, which are large aquatic rodents characterized by their massive skulls, devoid of post-orbital processes, with the angle of the lower jaw rounded, the molars rootless or semi-rooted, with re-entering enamel-folds, and one pair of premolars above and below.
The dentition includes one pair of premolars above and below, and rooted or rootless molars with but few enamel folds.
Dipodomys, which has the molars rootless, is typified by D.
- The mole-rats (Spalacidae) bring us to the mouselike section, or Myoidea, in which there are no premolars and the molars may be occasionally reduced to z; these teeth being either rooted or rootless, with either cusps or enamel-folds, and the first generally larger than the second.
The humerus lacks a foramen at the lower end; and the molar teeth, as explained and illustrated in the article Vole, consist of two longitudinal rows of triangular alternating vertical prisms, and may be either rootless or rooted.
In the circumpolar Evotomys (represented in England by the red-backed field-mouse) and the nearly allied North American Phenacomys, the molars develop roots in old age; but in Microtus (which includes the water-rat, and is circumpolar) they are rootless throughout life, the genus being' one of the largest in the mammalian class (see Vole).
The Octodontidae, which are exclusively South American, differ from the preceding family by the tympanic bulla being filled with cellular bony tissue, and by the par-occipital process curving beneath it, while the cheek-teeth are almost or completely rootless and composed of parallel plates.
Of these Ctenodactylus and Pectinator are characterized by the union of the incus and malleus of the internal ear, the free fibula and the almost rootless cheek-teeth.
Skull depressed, frontals contracted and without post-orbital processes; p.; or; molars rootless, with transverse enamel-folds.
These are regarded as representing a distinct family, the Saghatheriidae, characterized by the possession of the full series of twenty-two teeth in the upper jaw, among which the first pair of incisors was modified to form trihedral rootless tusks, while the two remaining pairs were separated from one another and from the teeth in front by gaps.
2), a rootless plant, which hangs in long grey lichen-like festoons from the branches of trees, a native of Mexico and the southern United States; the water required for food is absorbed from the moisture in the air by peculiar hairs which cover the (From The Botanical Magazine, by permission of Lovell, Reeve & Co.) FIG.