Page:EB1911 - Volume 14.djvu/672

Rh and affords a fixed point for the origins of the superficial cervical muscles.

The skull is long, with slender zygomatic arches; the nasal bones are strong and early become united, and in front of them the nostrils are continued forwards in tubes formed of thick cartilage, the septum between which becomes partially or wholly ossified beneath. There are 7 cervical, 13 dorsal, 6 lumbar, 6 sacral and 10-12 caudal vertebrae; of the dorsal and lumbar there may be one more or less. The sacral vertebrae are united by their expanded and compressed spinous processes, and all the others, with the exception of the cervical, are closely and solidly articulated together, so as to support the powerful propulsive and fossorial actions of the limbs. The upper incisors are simple chisel-edged teeth; the canine is long and two-rooted; then follow three subequal conical premolars, and a fourth, much larger, and like a canine; these are succeeded by three molars with W-shaped cusps. In the lower jaw the three incisors on each side are slightly smaller, and slant more forwards; close behind them is a tooth which, though like them, must, from its position in front of the upper canine, be considered as the canine; behind it, but separated by an interval, is a large double-rooted conical tooth, the first premolar; the three following premolars are like the corresponding teeth above, but smaller, and are succeeded, as above, by the three molars. See.

In the other members of the Talpinae, which are North American, the first upper incisor is much taller than the second. They include the curious star-nosed mole (Condylura cristata), which has the typical series of 44 teeth and a series of fleshy appendages round the extremity of the snout; the species known as Scapanus townsendi and Parascalops americanus, each representing a genus by itself, and characterized by the absence of nasal appendages and the presence of only two pairs of lower incisors; and, finally, Scalops aquaticus, in which the dentition is further reduced by the loss of the lower canine, the total number of teeth thus being forty.

Forming a transition to the subfamily Myogalinae, in which the clavicle and humerus are typically of normal form, and there is no sickle-shaped bone in the fore-foot, is the Chinese mole (Scaptonyx piscicauda), characterized by having the clavicle and humerus of the true mole-type, but the foot like that of the under-mentioned Urotrichus. The relative proportions of the first and second upper incisors are also as in Talpa, but there are only two pairs of lower incisors.

Among the more typical Myogalinae, mention may be made of Dymecodon pilirostris, from Japan, representing a genus by itself; nearly allied to which are the shrew-moles, as represented by the small and long-tailed Urotrichus of Japan, with incisors and premolars , and U. (Neurotrichus) gibbsi of North America, in which the premolars are. A still more interesting form is the Tibetan Uropsilus soricipes, a non-burrowing species, with the external appearance of a shrew combined with the skull of a mole, the feet being much narrower than in Urotrichus, and the dental formula i., c. , p. , m..

The typical representatives of the subfamily are the two European desmans, Myogale moschata and M. pyrenaica, which are aquatic in habits and have the feet webbed and the full series of 44 teeth. The former is by far the largest member of the whole family, its total length being about 16 in. Its long proboscis-like snout projects far beyond the margin of the upper lip; the toes are webbed as far as the bases of the claws; and the long scaly tail is laterally flattened, forming a powerful instrument of propulsion when swimming. This species inhabits the banks of streams and lakes in south-east Russia, where its food consists of various aquatic insects. M. pyrenaica, living in a similar manner in the Pyrenees, is much smaller, has a cylindrical tail, and a relatively long snout.

The Shrew-mice, or, shortly, shrews (Soricidae), are closely related to the Talpidae, with which they are connected by means of some of the subfamily Myogalinae. They are, however, distinguished by the ring-like tympanic, the incompleteness of the zygomatic arch, the tubercular-sectorial type of upper molar, the two-cusped first upper incisor, and the forward direction of the corresponding lower tooth. As a rule they are terrestrial, but a few are aquatic.

The dentition (fig. 5) is characteristic, and affords one of the chief means of classifying this exceedingly difficult group of mammals. There are no lower canines, and always six functional teeth on each side of the lower jaw, but in some rare instances an additional rudimentary tooth is squeezed in between two of the others. The first pair of teeth in each jaw differ from the rest; in the upper jaw they are hooked and have a more or less pronounced basal cusp; in the lower jaw they are long and project horizontally forwards, sometimes with an upward curve at the tip. Behind the first upper incisor comes a variable number of small teeth, of which, when all are developed, the first two are incisors, the third the canine, and the next two premolars; behind these, again, are four larger teeth, of which the front one is the last premolar, while the other three are molars. Thus we have in the typical genus Sorex (fig. 5) the dental formula i., c. , p. , m. , total 32, or twenty upper and twelve lower teeth. The lower formula, as already stated, is constant, but the number of the upper series varies from the above maximum of twenty to a minimum of fourteen in Diplomesodon and Anurosorex, in which the formula is i. 2, c. 1, p. 1, m. 3. From the relation of the fourth upper tooth to the premaxillo-maxillary suture it has been supposed that shrews, like many polyprotodont marsupials, have four pairs of upper incisors; but this is improbable, and the formula is accordingly here taken to follow the ordinary placental type.

Shrews may be divided into two sections, according as to whether the teeth are tipped with brownish or reddish or are wholly white, the former group constituting the Soricinae and the latter the Crocidurinae.

In the red-tipped group is the typical genus Sorex, which ranges over Europe and Asia north of the Himalaya Mountains to North America. There are twenty upper teeth with the formula given above, the ears are well developed, the tail is long and evenly haired, and the aperture of the generative organs in at least one of the sexes is distinct from the vent. The common shrew-mouse (Sorex araneus) has a distribution co-extensive with that of the genus in the Old World, and the North American S. richardsoni can scarcely be regarded as more than a local race. A few species, such as Sorex hydrodomus of Alaska and S. palustris of the United States, have fringes of long hairs on the feet, and are aquatic in habit. The latter has been made the type of the genus Neosorex, but such a distinction, according to Dr J. E. Dobson, is unnecessary. The same authority likewise rejects the separation of the North American S. bendirei as Atophyrax, remarking that this species is an inhabitant of marshy land, and appears to present many characters intermediate between S. palustris and the terrestrial species of the genus, differing from the former in the absence of well-defined fringes to the digits, but agreeing with it closely in dentition, in the large size of the infra-orbital foramen, and in the remarkable shortness of the angular process of the lower jaw. In India and Burma the place of Sorex is taken by Soriculus, in which the upper teeth are generally 18, although rarely 20, and the generative organs have an opening in common with the vent after the fashion of the monotreme mammals. The latter feature occurs in the North American Blarina, which is characterized by the truncation of the upper part of the ear and the short tail, the number of upper teeth being 20 or 18. Another American genus, Notiosorex, in which the ear is well developed and the tail medium, has only 16 upper teeth. From all the rest of the red-toothed group the water-shrew, Neomys (or Crossopus) fodiens, of Europe and northern Asia, differs by the fringe of long hairs on the lower surface of the tail; the number of upper teeth being 18.

In the white-toothed, or crocidurine, group, the small African genus Myosorex, which has either 18 or 20 upper teeth, includes long-tailed and large-eared species in which the aperture of the generative