The genus may be split up into subgenera corresponding with the above table; these subdivisions being sometimes accorded full generic rank. For instance the Japanese T. wogura and the Siberian T. robusta are often referred to under the ill-sounding titles of Mogera wogura and M. robusta.
 | |
| Fig. 3.—Skeleton of Mole (Talpaeuropaea) (lower jaw removed to showbase of skull). | |
c, Calcaneum. c.h, Clavicular articulation of the humerus. cl, Clavicle. e.c, External condyle of humerus. f, Femur. fb, Fibula. fc, Falciform bone (radial sesamoid). h, Humerus. i.c, Internal condyle of humerus. il, Left iliac bone. i.p, Ramus of the ilium and pubis. is, Ischium. l.d, Ridge of insertion of latissimus dorsi muscle. l.t, Lesser trochanter. | m, Manubrium sterni. o, Fourth hypapophysial sesamoid ossicle. ol, Olecranon. p, Pubic bone widely separated from that of the opposite side. pa, Patella. p.m, Ridge for insertion of pectoralis major muscle. pt, Pectineal eminence. r, Radius. rb, First rib. s, Plantar sesamoid ossicle corresponding to the radial sesamoid (os falciform) in the manus. sc, Scapula. s.h, Scapular articulation of the humerus. t, Tibia. u, Ulna. |
Referring more fully to the European species, it may be mentioned that the mole exhibits in its organization perfect adaptation to its mode of life. In the structure of the skeleton striking departures from the typical mammalian forms are noticeable. The first sternal bone is so much produced as to extend forward as far as a vertical line from the second cervical vertebra, carrying with it the very short almost quadrate clavicles, which are articulated with its anterior extremity and externally with the humeri, being also connected ligamentously with the scapula. The fore-limbs are thus brought opposite the sides of the neck, and from this position a threefold advantage is derived:—in the first place, as this is the narrowest part of the body, they add little to the width, which, if increased, would lessen the power of movement in a confined space; secondly this position allows of a longer fore-limb than would otherwise be possible, and so increases its lever power; and, thirdly, although the entire limb is relatively short, its anterior position enables the animal, when burrowing, to thrust the claws so far forward as to be in a line with the end of the muzzle, the importance of which is evident. Posteriorly, we find the hind-limbs removed out of the way by approximation of the hip-joints to the centre line of the body. This is effected by inward curvature of the innominate bones at the acetabulum to such an extent that they almost meet in the centre, while the pubic bones are widely separated behind. The shortness of the fore-limb is due to the humerus, which, like the clavicle, is so reduced in length as to present the appearance of a flattened X-shaped bone, with prominent ridges and deep depressions for the attachments of powerful muscles. Its upper extremity presents two rounded prominences; the smaller, the true head of the bone, articulates as usual with the scapula; the larger, which is the external tuberosity rounded off, forms a separate joint with the end of the clavicle. This double articulation gives the rigidity necessary to support the great lateral pressure sustained by the fore-limb in excavating. The bones of the fore-leg are normal, but those of the fore-foot are flattened and laterally expanded. The great width of the fore-foot is also partly due to the presence of a peculiar bone on the inner side of the palm and articulating with the wrist.
The muscles acting on these modified limbs are homologous with those of cursorial insectivora, differing only in their relative development. The tendon of the biceps traverses a long bony tunnel, formed by the expansion of the margin of the bicipital groove for the insertion of the pectoralis major muscle; the anterior division of the latter muscle is unconnected with the sternum, extending across as a band between the humeri, and co-ordinating the motions of the fore-limbs. The teres major and latissimus dorsi muscles are of immense size, inserted into the prominent ridge below the pectoral attachment, and are the principal agents in the excavating action of the limb. The cervical muscles connecting the slender scapulae, and through them the fore-limbs, with the centre line of the neck and with the occiput are large, and the ligamentum nuchae between them is ossified. The latter condition appears to be due to the prolongation forwards of the sternum, preventing flexion of the head downwards; and accordingly, the normal office of the ligament being lost, it ossifies, 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 [Mole].
| Fig. 4.—Russian Desman (Myogale moschata). |
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 2⁄1 and premolars 4⁄3, and U. (Neurotrichus) gibbsi of North America, in which the premolars are ¾. 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. 2⁄1, c. 1⁄1, p. 3⁄3, m. 3⁄3.
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.