Word Finder - molars

definition

A back tooth having a broad surface used for grinding one's food.

definition

A unit of concentration equal to one mole per litre.

These three are therefore reckoned as milk-molars, and their successors as premolars, while the last three correspond to the true molars of other mammals.

Molars in general characters resembling those of Sarcophilus, but of more simple form, the cusps being less distinct and not so sharply pointed.

In the upper molars the two outer columns or tubercles of the primitive tubercular molar coalesce to form an outer wall, from which proceed two crescentic transverse crests, the connexion between the crests and the wall being slight or imperfect, and the crests themselves sometimes tubercular.

In Europe the group is represented by the long-known and typical genus Lophiodon with three premolars in each jaw, of which the upper are simpler than the molars.

In the New World the porcupines are represented by the members of the family Erethizontidae, or Coendidae, which have rooted molars, complete collar-bones.

The teeth are usually differentiated into incisors, canines and molars.

The lower molars resemble generally those of the upper jaw, but are narrower.

In India also occurs Hippohyus distinguished by the extremely complicated structure of its molars.

In the European Miocene we have Hyotherium and Palaeochoerus, and in the Upper Oligocene Propalaeochoerus, which have square molars without any tendency to a selenodont structure in their cusps.

Choeropotamus is a European Oligocene genus with bunodont molars which show a conspicuous basal cingulum in the lower dentition; the first premolar is absent.

In the European Miocene Listriodon, which also occurs in the Indian Tertiaries, the molars have a pair of transverse ridges, like those of the proboscidean Dinotherium; but the genus is believed to be related to the Oligocene Doliochoerus and Choerotherium, in which these teeth show a more normal type of structure.

The premolars and molars may be rooted or rootless, with tuberculated or laminated crowns, and are arranged in an unbroken series.

The mouth is divided into two cavities communicating by a narrow orifice, the anterior one containing the incisors and the posterior the molars, the hairy skin of the face being continued inwards behind the incisors.

In this the crowns of the molars are more or less shortened, with their cusps either arranged in longitudinal lines, or forming four upper and three lower more or less distinct oblique ridges.

The Nannosciurinae, or second sub-family of Sciuridae, are represented only by the pigmy squirrels (Nannosciurus), characterized by their very short-crowned molars (which approximate to those of dormice in structure) and small premolars, of which the first upper pair is often deciduous, while the upper molars have only three oblique ridges.

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 well-known Indian palm-squirrel, Funambulus palmarum, typifies an Indo-Malay genus allied to Xerus in skull-characters but with molars more like those of Sciurus.

The upper molars are subequal, each with one internal and two external.

The dentition includes one pair of premolars above and below, and rooted or rootless molars with but few enamel folds.

Perognathus and Heteromys have rooted molars; the latter genus is distinguished by the presence of flattened spines among the fur, and has species extending into South America.

In general habits and appearance these animals recall large jerboas, from which group they are, however, distinguished by the four pairs of rooted cheek-teeth, the premolars being as large as the molars, and the latter having one outer and one inner enamel-fold.

In the dormice, forming the section Myoxidea, with the single family Gliridae (or Myoxidae), a single pair of premolars may or may not be present; the molars are short-crowned and rooted, with transverse From de Winton.

The Dipodinae, on the other hand, are leaping rodents, with the metatarsals elongated, a small upper premolar present or absent, and the crowns of the molars tall.

The Spalacidae are burrowing types, allied apparently to the ancestral Jaculidae, and characterized by the second and third molars being equal in size, the presence of enamel-folds in all these teeth, and the superiority in size of the claws of the second, third and fourth front toes over the other two.

The genus Nesocia is like Mus, but with the incisors and molars broader, and the transverse laminae of the latter more clearly defined.

Australia is the home of the group of jumping species, known as jerboa-rats, characterized by the elongation of the hind limbs, arranged under the genera Notomys, Dipodillus, Ammomys and Conilurus, distinguished from one another by the structure of the molars and the number of teats and foot-pads, the second being further characterized by its long ears.

Here also may be noticed the huge Philippine long-haired rats of the genus Phlaeomys, characterized by their broad incisors, transversely laminated molars and large claws.

There are three pairs of rooted molars, whose crowns carry transverse plates, decreasing in number from three in the first to one in the last tooth.

The last representatives of the Muridae are confined to Australasia and the Philippines, and constitute the sub-family Hydromyinae, characterized by the very general presence of only two pairs of molars in each jaw.

In the typical Australian and Papuan Hydromys, locally known as water-rats, the molars originally have transverse ridges, the enamel folds between which form cutting edges whose sharpness depends upon the degree to which the teeth have been worn, while the large hind feet are webbed.

Still less specialized are Chrotomys and Xeromys, which include Philippine land-rats, while Crunomys, from the sane area, retains the third molars, and thus connects the group with the Murinae.

Finally, the Philippine Rhynchornys is represented by a rat with two pairs of molars and a long shrew-like nose, the zygomatic arch of the skull being also placed unusually far backward.

At least one pair of premolars is present in each jaw; and these teeth and the molars typically have one outer and one inc_e.

Fore-feet with four digits, hind-feet with three; clavicles imperfect; molars divided by enamel-folds into transverse lobes; milk-teeth shed before birth.

The jugal is without an inferior angle, and extends forwards to the lachrymal; the palate is contracted in front and deeply emarginate behind; the incisors are short, and the molars divided by continuous folds into transverse plates; and the two halves of the lower jaw are welded together in front.

Aconaemys is an allied Chilean genus in which the enamel-folds meet across the molars.

Skull depressed, frontals contracted and without post-orbital processes; p.; or; molars rootless, with transverse enamel-folds.

In America, Paramys, with transversely ridged molars, is allied; and the European Sciuromys should perhaps find a place in the same neighbourhood.

A more advanced phase is represented in the European Lower Oligocene by the Pseudosciuridae, with the genera Pseudosciurus, Sciuroides, Trechomys, Theridomys, &c., in which part of the masseter passes through the broad infra-orbital canal, and the premolars are; the molars being low-crowned, many-rooted and either cusped or ridged.

In general dental characters, especially the retention of three pairs of molars, this genus approximates to the Leporidae, although in the absence of post-orbital processes and the pattern of the molars it departs less widely from the modern Ochotonidae than does Prolagus.

The canine was like a premolar, and in contact with the first tooth of that series; and the cheek-teeth were short-crowned, with the premolar simpler than the molars, and a third lobe to the last lower tooth of the latter series.

The earlier forms had the full series of 44 teeth, with the premolars simpler than the molars; but in the later types the canines and some of the incisors disappear, and at least the hinder premolars become molar-like.

The upper jaw is apparently destitute of incisor and canine teeth, but possesses five molars on each side, with a corresponding number in the jaw beneath.

The molars, and more especially the last, are smaller and simpler than in the pigs of the genus Sus, but the peculiarity of this genus is the extraordinary development of the canines, or tusks, of the male.

The cheek-teeth are low-crowned, with the external cones of the upper molars fused into a W-like outer wall, and the inner ones retaining a regular conical form; while in the lower teeth the crown is formed of crescentic ridges, of which there are three in the last and two each in the other teeth.

Titanotherium, of the Oligocene of the Dakotas and neighbouring districts, was a huge beast, with the hinder upper premolars similar in character to the molars, a pair of horn-cores, arising from the maxilla, overhanging the nose-cavity, four front and three hind toes, only twenty dorso-lumbar vertebrae, and an almost continuous and unbroken series of teeth, in which the canines are short; the dental formula being i.

The skull, which has a longer face than in Titanotherium, lacks horn-cores, while all the upper premolars are simpler than the molars, and the full series of 44 teeth was present.

The first of these is the common shoa 1 tailed field-mouse, or "field-vole," Microtus agrestis, which belongs to the typical section of the type genus, and M S is about the size of a 343 mouse, with a short stumpy body, and a Upper and Lower Molars of the Water-Rat tail about one-third the (or Water-Vole), Microtus amphibius.

On account of an important difference in the structure of its molars, it is now very generally referred to a distinct genus, under the name of Evotomys glareolus; these teeth developing roots at a certain stage of existence, instead of growing permanently.

Fossil voles from the Pliocene of England and Italy with molars which are rooted as soon as developed form the genus Mimomys.