1902 Encyclopedia > Mole

Mole




MOLE (contracted form of mould-warp, i.e., mould-caster), a term restricted in England to the common mole (Talpa europszd), a small, soft-furred, burrowing mammal, with minute eyes, and broad fossorial fore feet, belonging to the order Insectivora and family Talpidx, but generally applied elsewhere to any underground burrowing animal of the class Mammalia. Thus, in North America we find, representing the same family, the star-nosed moles (Con-dylurd), and the shrew moles (Scalops and Scapanus); in South Africa, the golden moles of the far-removed family Chrysochloridx; and in South-East Europe, Asia, and South Africa, the rhizophagous rodent moles of the order Bodentia and families Spalacidx and Muridee (see MAMMALIA, vol. xv. pp. 405, 419, figs. 64 and 96).

Talpa europixa, the Common Mole, type of the genus Talpa} is about six inches in length, of which the tail measures somewhat more than an inch; the body is long and cylindrical, and, owing to the very anterior position of the forelimbs, the head appears to rest between the shoulders; the muzzle is long and obtusely pointed, ter-minated by the nostrils, which are close together in front; the minute eye is almost hidden by the fur; the ear is without a conch, opening on a level with the surrounding integument; the forelimbs are rather short and very mus-cular, terminating in broad, naked, shovel-shaped feet, the palms normally directed outwards, each with five subequal digits armed with strong flattened claws ; the hind-feet, on the contrary, are long and narrow, and the toes are provided with slender claws. The body is densely covered with soft, erect, velvety fur,—the hairs uniform in length and thickness, except on the muzzle and short tail, the former having some straight vibrissas on its sides, whilst the latter is clothed with longer and coarser hairs. The fur is generally black, with a more or less greyish tinge, or brownish-black, but various paler shades up to pure white have been observed.

The food of the mole consists chiefly of the common earth-worm, in pursuit of which it forms its well-known underground excavations. Its habits, so difficult to observe, were many years ago most patiently studied and described by M. Henri le Court. Like many other mammals the mole has a lair or fortress to which it may retire for security. This is constructed with much ingenuity. It consists of a central nest formed under a hillock which is placed in some protected situation, as under a bank, or between the roots of trees. The nest, which is lined with dried grass or leaves, communicates with the main-run by four passages, one of which only joins it directly, leading downwards for a short distance and then ascending again; the other three are directed upwards and communicate at regular intervals with a circular gallery constructed in the upper part of the hillock, wdiich in turn communicates by five passages leading downwards and outwards with another much larger gallery placed lower down on a level with the central nest, from which passages proceed outwards in different directions, one only communicating directly with the main-run, while the others, curving round, soon join, or end in culs-de-sac. The main-run is somewhat wider than the animal's body, its walls are smooth, and formed of closely compressed earth, its depth varying according to the nature of the soil, but ordinarily from four to six inches. Along this tunnel the animal passes backwards and forwards several times daily, and here traps are laid by mole-catchers for its capture. From the main-run numerous passages are formed on each side, along which the animal hunts its prey, throwing out the soil in the form of mole-hills. The mole is the most voracious of mammals, and, if deprived of food, is said to succumb in from ten to twelve hours. Almost any kind of flesh is eagerly devoured by captive moles, which have been seen by various observers, as if maddened by hunger, to attack animals nearly as large as themselves, such as birds, lizards, frogs, and even snakes; toads, however, they will not touch, and no form of vegetable food attracts their notice. If two moles be confined together without food, the weaker is invariably devoured by the stronger. They take readily to the water— in this respect, as well as in external form, resembling their representatives on the North American continent. Bruce, writing in 1793, remarks that he saw a mole paddling towards a small island in the Loch of Clunie, 180 yards from land, on which he noticed molehills.

The sexes come together about the second week in March, and the young—generally from four to six in number—which are brought forth in about six weeks, quickly attain their full size.

The mole exhibits in its whole organization the most perfect
adaptation to its peculiar mode of life. In the structure of the
skeleton very striking
departures from the
typical mammalian
forms are noticeable.
The first sternal bone
is so much produced
anteriorly as to extend
forward as far as a
vertical line let down
from the second cervi-
cal vertebra, carrying
with it the very short
almost quadrate cla-
vicles, which are arti-
culated with its an-
terior extremity and
distally with the hu-
meri, being also con-
nected ligamentously
with the scapula?. The
forelimbs 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 but
little to the general
width, which, if in-
creased, would lessen
the power of move-
ment in a confined
space ; secondly, this
position allows of a
longer forelimb than
would otherwise bo
possible, and so in-
creases its lever power;
and, thirdly, although
the entire limb is rela-
tively very short, its
anterior position en- Skeleton of Mole x £ (lower jaw removed to
ables the animal, when show base of skull),
burrowing to thrust e, calcaneum; c.Ji., clavicular articulation of the
+1IA plnwc cn for- fnv humerus; el., clavicle; e.c, external condyle of hu-
me ciaws so iar IOI- MERUS. ^ TEMUR; p,t flrjula. yc> faiciform hone
ward as to be m a line (radial sesamoid); h, humerus; i.c, internal condyle
with the end of the of humerus; il, left iliac hone; i.p, ramus of the
muzzle, theimportance ilium and pubis ; is., ischium ; Id ridge of insertion
« , . , . r . , , l of latissimus dorsi muscle; l.t, lesser trochanter;
ot w men is evident. m> manubrium sterni; o, fourth hypapophysial se-
Posteriorly,w efind the samoid ossicle; ol, olecranon ; p., pubic bone widely
hind limbs similarly separatedfromthatoftneoppositeside;pa.,patella;
™.„j „,.f nf p.m., ridge for insertion of pectoralis major muscle ;
remcrvea our oi tilt pectineal eminence; r, radius; rb, first rib; s, way by approximation plantar sesamoid ossicle corresponding to the radial of the hip-joints to sesamoid (os falciform) in the manus; sc., scapula; the centre line of the s-^'' scaPular articulation of the humerus; t, tibia; body. This is effected "' u na'
by inward curvature of the innominate bones at the acetabula to such an extent that they almost meet in the centre, while the pubic bones are widely separated behind.2 The shortness of the
1 It is most interesting to observe how, in the golden moles (Chrysoehloridm) of South Africa, the necessary modifications of the corresponding parts of the body and limbs fitting them for fossorial action and underground progression have been brought about in a totally different manner. In them the manubrium sterni is not anteriorly elongated, neither are the clavicles shortened ; but this is made up for by a deep hollowing out of the antero-lateral walls of the thorax, the ribs in these parts and the sternum being convex inwards, the long clavicles have their distal extremities pushed forward, and the concavities on the sides and inferior surface of the thorax lodge the thick muscular arms.

2 In Jaeohs's Talpm Europese Anatome (Jena, 1816) this part of the pelvic wall (marked pt in the fig.) was identified with the symphysis forelimb is due to the humerus, which, like the clavicle, is so much reduced in length as to present the appearance of a flattened X-shaped bone, with prominent ridges and deep depres-sions for the attachments and origins of the powerful muscles connected with it. Its proximal extremity presents two rounded prominences : the smaller, the true head of the bone, articulates as usual with the scapula?; the larger, which is really the external tuberosity rounded off, forms a separate synovial joint with the end of the clavicle. This double articulation gives to a naturally loose joint the rigidity necessary to support the great lateral pressure sustained by the forelimb in excavating. The forearm bones are normal, but those of the forefeet are much flattened and laterally expanded. The great width of the forefoot is also partly due to the presence of a peculiar falciform bone, lying on the inner side of the palm and articulating by its proximal extremity with the wrist. Into the radial side and under surface of this bone is inserted a tendon derived from that of the palmaris longus muscle, which, acting upon it as an abductor, separates it from the side of the palm, and so increases the width of the latter, at the same time rendering the palmar integument tense.

The muscles acting on these remarkably modified limbs are all homologous with those of the cursorial insectívora, differing only in their relative development. The tendon of the biceps traverses a long osseous tunnel, formed by the great expansion of the margin of the bicipital groove for the insertion of the large pectoralis major muscle ; the anterior division of the latter muscle is unconnected with the sternum, extending across as a muscular band between the humeri, and co-ordinating the motions of the forelimbs. The teres major and latissimus dorsi muscles are of immense size, probably relatively larger than in any other mammal, and are inserted to-gether into the prominent ridge below the pectoral attachment; they are the principal agents in the excavating action of the limb. The cervical muscles connecting the slender scapula;, and through them the forelimbs, with the centre line of the neck and with the occiput are large, and the ligamentum nucha; between them is ossified (as in all true moles); the latter condition appears to be due to the prolongation forwards of the sternum (described above), preventing all flexion of the head downwards; and, accordingly, the normal office of the ligament being lost, it ossifies, and so affords a more 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 sep-tum between which becomes partially or wholly ossified beneath. There are 7 cervical, 13 dorsal, 6 lumbar, 6 sacral, and 10-12 caudal vertebra; ; of the dorsal and lumbar there may be one vertebra more or less. The sacral vertebra; are united by their greatly ex-panded and laterally compressed spinous processes, and all the others, with the exception of the cervical, are very closely and solidly articulated together, so as to support the powerful propulsive and fossorial actions of the limbs. Dentition: i. _§, c T, prm. -|, m. •§, x 2 = 44 teeth. 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 quite like them, must, from its position in front of the upper canines when the jaws are closed, be considered as the canine ; behind it, but separated by an interval, is a largo double-rooted conical tooth, the first premolar ; the three following premolars are like the corre-sponding teeth above, but smaller, and are succeeded, as above, by three molars.

The geographical distribution of the common mole may be said
to exceed that of all the other known species of the genus to which
it belongs taken together. It extends from England to Japan,
and from the Dovre-Fjeld Mountains in Scandinavia and the Middle
Dwina region in Russia to southern Europe and the southern slopes
of the Himalayas, where it occurs at an elevation of 10,000 feet.
In Great Britain it is found as far north as Caithness, but in Ireland
and in the Western Isles of Scotland (except Mull) it is altogether
unknown. (G. E. D.)



Footnotes

608-1 Eight species may be recognized, and arranged, according to their

609-1






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