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Proboscis.

Proboscis.

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defined from the outer side); it divides the frenulum longitudinally
. Also in Talpa there is on the ventral side of the proboscis
a distinct naked furrow, which posteriorly widens out.

The proboscides of the Tapir, and of the Elephant, are externally
, on the whole, formed as in the other Mammals with a
proboscis. In the Tapir (PL 17, fig. 13) the nostrils situated at
the end of the proboscis are surrounded by a naked area, from
which proceeds a longitudinal naked stripe on the ventral side
of the proboscis, which stripe — the longitudinal furrow of other
proboscidiferous Mammals — grows broader posteriorly and is
continued without sharp demarcation by the mucous side of the
upper lip, which has an oblique direction. The said mucous side
is not directly continued into the hard palate. As in the Dog etc.
there is a gingiva and incisors between both.

In the Elephant (PI. 17, fig. 14) the area round the nostrils
is hairy as in many other Mammals. The furrow on the ventral
side of the proboscis is most distinct and narrowest near the
distal end, where it is also naked as usual; proximad it becomes
less sharply defined and hairy. At the proximal end the under
side of the proboscis is continued directly into the mouth; the
hairy surface is continued unto the margin of the intermaxillary
bone, and the mucous side of the lip has totally disappeared.

But though the proboscis of the Elephant, as well as that of
the Tapir, in its outer appearance is not substantially different
from that of other Mammals, the case is quite otherwise in so
far as the inner constitution of the proboscis is concerned. In all
the proboscidiferous Mammals examined, exc. the Tapir and Elephant
, we find that the nasal cartilage is continued unto the apex
throughout the whole proboscis. In Sus the nasal cartilage is
almost immovably connected with the skull, and only the skin
on the apex of the proboscis is movable, through the action of
the m. maxillo-labialis, whose tendons end in it. In Talpa and
Macroscelides we have found the nasal cartilage partially calcified,
and the mobility of the proboscis is therefore certainly nor very
extensive in these animals. In Nasua the nasal cartilage is rao-
vably connected with the skull and the mobility probably somewhat
greater. But on the whole the mobility of the proboscis in
the proboscidiferous Mammals, exc. the Tapir and the Elephant, is
rather limited. In all those Mammals (PL 14, fig. 1) the proboscis
is principally constituted by the nasal cartilage and the skin, between
which run the tendons of the m. maxillo-labialis, numerous
nerves (branches of trigeminus) etc.; while muscular tissue is very
scarce (parts of m. nasalis etc. may be found in the proboscis).

In the Elephant and Tapir the nasal cartilage does not extend
into the proboscis; only the posterior end thereof, hard on the nasal
bones, is present, and the proboscis is composed only of epithelium,
connective tissue and muscles (and of nerves, vessels and — in the
Tapir — of glands): PL 14, fig. 2—3. The flexibility of the trunk
has in this manner been greatly augmented, and such an instrument
could then be developed, as the trunk of the Elephant,
which is able to be moved in all directions with the greatest
ease, to be spirally rolled up, to be shortened and lengthened etc.

And in this flexible proboscis of the Elephant and the Tapir
the muscles have been evolved in a manner quite different from
what is found in other proboscidiferous Mammals. In all save
the Elephant and the Tapir the general arrangement is such, that
a number of thin tendons belonging to the m. maxillo-labialis go
to the end of the trunk; between them, project the branches of
the m. nasalis. In the Elephant, which we will first take into
consideration, the m. maxillo-labialis still plays an important part
in the movements of the trunk, but it is wholly fleshy and extends
as a fleshy mass divided into numerous bundles throughout the
whole length of the trunk to its distal end. And other muscles
participate in the formation of the muscular system of the trunk:
the pars rimana and the pars supralabialis m. buccinatorii and the
numerous mm. recti going between the mucous membrane of the
nasal tubes and the skin. In this manner the whole proboscis
of the Elephant is in the main a fleshy mass, the constitution of
which may be compared with such an organ as the tongue of the
Mammals : while the proboscis of most other Mammals is mainly
composed of cartilage and connective tissue in various forms
(tendons etc.).

Thus the proboscis of the Elephant has become a prehensile
organ. For such is the biological meaning of all this : in other
Mammals with a proboscis (exc. the Tapir) this organ is tactile
in function, sometimes also an organ which may be used to root
about in loose material; but not a prehensile organ at all; while
in the Elephant, the faculty of serving as a tactile organ being
retained, the prehensile functions have taken the first place and
have reached a state of high perfection. The final touch, so to
speak, in perfecting the proboscis of the Elephant we find in the
well-known particularity of the end thereof, which is peculiar in
that the septum between the nasal tubes stops short, a little before
the end of the proboscis, the distal ends of the nasal tubes
being here for a short distance confluent. At the end of the
proboscis thus there is only one hole, surrounded by a liplike
border, whose ventral and dorsal regions — the last with the well-
known short prolongation — may be moved against each other,
the end of the proboscis thus being enabled to grasp small objects.
But other parts of the proboscis have also an extraordinary faculty
for prehension.

The proboscis of the Tapir, because of its shortness, cannot
perform such feats as that of the Elephant can accomplish; but
it is developed on similar lines. It is a highly muscular body, in
which the muscular tissue, represented by numerous mm. recti,
the m. maxillo-labialis, nasolabialis and pars rimana, contributes
a considerable portion of the whole mass, without having, however
, such a share in the composition of the trunk as in the
Elephant, a considerable part of the place within the wall of the
proboscis being filled with glands opening into the nasal tubes,
or into the mouth. It may also be noted, that the muscles of the
proboscis are in this animal of a far less complicated structure,
have to a much slighter degree been differentiated, than in the
Elephant. But the proboscis in the Tapir is also a grasping,
prehensile organ.

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