Thank goodness the molar nightmare was over.
The more specialized of the two species is the Indian or Asiatic elephant, Elephas maximus, specially characterized by the extreme complexity of the structure of its molar teeth, which are composed of a great number of tall and thin plates of enamel and dentine, with the intervals filled by cement (see Proboscidea, fig.
The average number of plates of the six successive molar teeth may be expressed by the "ridge-formula" 4, 8, 12, 12, 16, 24.
The molar teeth are of coarse construction, with fewer and larger plates and thicker enamel; the ridge-formula being 3, 6, 7, 8, io; while the plates are not flattened, but thicker in the middle than at the edges, so that their worn grinding-surfaces are lozengeshaped.
Cinereus), differs from all other members of the squirrel-family by its tall-crowned molar teeth.
- Upper Molar of Mastodon arvernensis, viewed from below.
Outer columns of upper molars similar, the hinder ones not flattened; ridges of lower molars oblique or directly transverse, a third ridge to the last molar in the earlier forms. The Lophiodontidae, which date from the Eocene, come very close to Hyracotherium in the horse-line; and it is solely on the authority of American palaeontologists that the division of these early forms into equoids and tapiroids is attempted.
Lophiodochoerus apparently represents this stage in the European Lower Eocene; Isectolophus, of the American Middle Eocene, represents a distinct advance, the last upper premolar becoming molar-like, while a second species from the Upper Eocene is still more advanced; the third lobe is, however, retained in the last lower molar.
6 a Oligocene of both hemispheres appears Protapirus, which ranges well into the Miocene, and is essentially a tapir, having lost the third lobe of the last lower molar, and being in process of acquiring molar-like upper premolars, although none of these teeth have two complete inner columns.
The next stage is Helaletes, also of Middle Eocene age, in which the first lower premolar has disappeared, and the last two upper premolars have become molar-like.
The lower cheekteeth have, unlike those of the Tapiroidea, crescentic ridges, which have not the loops at their extremities characteristic of the advanced Hippoidea; the last lower molar has no third lobe.
With the exception of the first lower premolar, the dentit i on is complete; the incisors being normal, but the canine rudimentary, and the last upper molar distinctly triangular.
The incisors tend to become latera l, the canines are enlarged, and the last upper molar is sub-quadrangular.
They differ from the other American monkeys in having one pair less of molar teeth in each jaw.
- Section of Upper Molar Teeth of Megatherium.
Unlike the Bovinae, there are frequently glands in the feet; and the upper molar teeth differ from those of that group in their narrower crowns, which lack a distinct inner column.
It is chiefly by the characters of the molar teeth that the various extinct modifications of the elephant type are distinguished.
- Grinding surface of Upper Molar Tooth of the7Mammoth (Elephas primigenius).
In later memoirs Reynolds followed up this subject by proceeding to establish definitions of the velocity and the momentum and the energy at an element of volume of the molecular medium, with the precision necessary in order that the dynamical equations of the medium in bulk, based in the usual manner on these quantities alone, without directly considering thermal stresses, shall be strictly valid - a discussion in which the relation of ordinary molar mechanics to the more complete molecular theory is involved.
UNGULATA, the name of an order of placental mammals in which the terminal joints of the toes are usually encased in solid hoofs or covered with broad hoof-like nails, while the molar (and not unfrequently some or all of the premolar) teeth have broad tuberculated crowns adapted for crushing vegetable substances.
The upper premolar and molar teeth are not alike, the former being single and the latter two-lobed; and the last lower molar of both first and second dentition is almost invariably threelobed.
As regards the teeth, we have the passage of a simply tubercular, or bunodont ((30vv6s, a hillock) type of molar into one in which the four main tubercles, or columns, have assumed a crescentic form, whence this type is termed selenodont (v€X vn, the new moon).
The primitive Artiodactyla thus probably had the typical number (44) of incisor, canine and molar teeth, brachyodont molars, conical odontoid process, four distinct toes on each foot, with metacarpal, metatarsal and all the tarsal bones distinct, and no frontal appendages.
13, B); in the upper teeth the outer cusps and in the lower the inner ones are the higher, and when worn the crown surfaces show oblique dentineareas; in shape the third molar is like the second, but it is smaller.
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 some cases the molar-formula is 3.