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13 Mammals generally.

origin extends above the foramen infraorbitale. The two portions
are fused into one; the part corresponding to the upper portion
in the Dog is anteriorly split up into several strong tendons, of
which the uppermost, and strongest, is inserted into the hinder
end of the nasal cartilage; while the rest are inserted into the skin
behind the nostril. That part of the muscle which corresponds
to the inferior portion in the Dog ends fleshy, as in this animal.

The m. maxillo-labialis of Talpa (PI. 15, fig. 1) is particularly
interesting inasmuch as its origin has moved much farther back
on the head than in any of the Mammals yet mentioned; the
muscle arises from the skull above the bony ear-opening and extends
outside the zygoma between the m. temporalis and masseter,
all three muscles forming together one muscular cushion on the
side of the head. The muscle is composed of several narrow,
loosely connected, muscle-bellies, which may easily be separated
by dissection. One of them, which is, as it were, ensheathed by
the others, is continued into a strong tendon, which goes to the
upper side of the nose; at the posterior end of the cartilaginous
nose this tendon is united with that of the other side and is
continued as a flat ribbon onto the fore end of the proboscis.
Of the other small muscle-bellies the lowermost is continued
into the strongest tendon, which goes to the ventral side of the
proboscis and ends not far from its tip near that of the other
side (but separate). The rest, three in number, are also each
continued into a long thin tendon, lying laterally on the proboscis
and ending towards its tip1). (Gomp. also the transverse
section of the proboscis of the mole, PI. 14, fig. 1).

In Echidna there is no m. maxillo-labialis, a lack which may
be the consequence of the slight mobility of the snout.

4. BUCCINATOR-GROUP.

The muscles, which we unite under this head, form the bulk
of the cheek and the lips.

In Echidna (PI. 10, fig. 1) the group is represented by the
buccinator muscle alone, whose fibres have a transverse (dorso-
ventrad) direction, going from the upper to the lower jaw; the
foremost fibres are bent, the convexity to the rear, the upper
and lower ends thereof being directed into the lips, which are,
as is well known, very feebly developed in Echidna.

From a buccinator similar to that of Echidna the more complicated
conditions found in other Mammals may probably be
derived. The starting point is as follows (comp. PL 17, fig. 3): in
the cheek there is found a layer of transverse fibres somewhat
bent, the convexity caudad; the ends of these fibres are connected
with the upper and lower jaw; the foremost of them have no
such connection, but are bent forwards into the upper and the
lower lip. But in such simplicity the buccinator is not found in
the Mammals apart from the Monotremata; always there are
rather considerable complications.

In Halmaturus (PI. 13, fig. 2—3), at a first glance, the conditions
appear to be of a primitive character, but on closer inspection
we find that here already are complications. The superficial
fibres of the buccinator are rather well adapted to the scheme,
being transverse; and also deeper lying bundles have the same
or a similar direction; but still deeper, near the mucous membrane
, there are fibres going at right angles to the others, having
thus a more longitudinal direction. Near the anterior end of the
muscle the anterior ends of the maxillo-labialis and platysma are
inserted into it. The fibres of the buccinator lying outside the
ends of the said muscles are those, which are bent into the upper
and the lower lip; we term them pars rimana buccinatorii.
In the upper lip there is still a very large part of buccinator-
fibres lying inside the pars rimana; these fibres have another
direction, viz. transverse (dorso-ventrad): pars supralabialis buccinatorii
(PI. 13, fig. 3). — The ends of the buccinator-fibres are on
some places inflected, following the mucous membrane and being
inserted on the jaws near the teeth; this is the case with the

*) In Myogale moschata the muscle agrees almost exactly with that of Talpa;
it takes its origin in the same place (above and a little behind the ear), has the
same relation to the other muscles and is composed of five small muscular bellies,
which all behave as in Talpa.

M. maxillo-labialis. Buccinator-group. 14

hind part of the supralabialis-bundles and with most of the
bundles of the cheek-portion of the buccinator; but other fibres,
viz. the front part of the supralabialis and the upper ends of
the front part of the cheek-portion, have a simple dorso-ventrad
direction, being inserted on the jaw farther above. — Within the
pars supralabialis lies the musculus nasalis (PI. 13, fig. 3). It is a flat
muscle, which takes its origin from the intermaxillar}^ bone, near
the teeth, and passes close to the bone upward; it is somewhat
expanded at the top, the fibres ending in the skin. In an analogous
manner, on the lower jaw, below the incisors, arises the
m. mentalis (PL 13, fig. 3), which also lies close to the bone; from
their origin the fibres pass downwards, and somewhat backwards,
and terminate in the skin of the lower jaw. Whether these two
muscles are differentiated parts of the buccinator or not we are
not able to decide. But we think it probable that they are.

As we have mentioned above, in Halmaturus some of the
deeper fibres of the buccinator have taken another, more longitudinal
direction than the rest, which have a transverse direction;
a distinct stratification of the muscle has not yet been evolved.
In the Ungulata (PL 16) which we have examined this has gone
further, the muscle being universally divided in two, distinct
layers, the superficial one of which consists of fibres which have
mainly a transverse direction, while the deeper layer generally
has a longitudinal direction; both layers are generally in some
places, especially at the hind end, intimately connected. The
fibres of the transverse layer may be partially interrupted in the
middle by a longitudinal inscriptio tendinea (Horse, PL 8, fig. 1).
Sometimes there may be a third, and deepest layer, partly transverse
, partly longitudinal (Zebu, Tapir, PL 16, fig. 11, Horse, PL 16,
fig. 14). Further we note, that from the ventral border of the
buccinator some longitudinal, superficial bundles have to a certain
degree separated from the rest of the muscle and taken a
direction into the median parts of the lower lip: m. depressor labii
inferioris (PL 16, fig. 3, 5, 7,12,15). The pars rimana is as in Halmaturus
a continuation of the transverse buccinatorius-layer; but sometimes
also the deep, longitudinal layer concurs into the formation
of it (Wapiti, Zebu and others). Sometimes (Horse) the pars rimana
forms a real sphincter, in others the anterior ends of the
bundles end in a fibrous median portion of the lips. There is
generally a well-developed pars supralabialis (PL 16, fig. 2, 4, 6 etc.;
PL 6), consisting as in Halmaturus of transverse fibres; it appears
generally as a continuation of the longitudinal buccinatorius-layer,
whose bundles take a different direction in the upper lip; in Sus
it is reduced. — The m. nasalis is in the Ungulata rather strongly
developed, being in most Artiodactyla (PL 11, fig. 1 and 5) divided
into several layers, which take their origin successively from the
lower margin of the intermaxillary bone and further above (and
sometimes also from the soft nasal wall or from the nasal cartilage
); the layers are partly separated by the tendons of the
maxillo-labialis. — Also the m. mentalis (PL 5, 6) is well developed
, and may, in the Artiodactyla, be divided into layers as
the m. nasalis; in others it may radiate diffusely into the skin.

As a further instance we may take the buccinator of the
Dog (PL 16, fig. 17). The cheek-portion of the muscle is short,
the mouth-cleft going far back. The superficial layer consists of
fibres, which are all bent into the upper and the lower lip, the
part of the muscle lying in the upper lip being far stronger than
that in the lower lip; the posterior bundles are interrupted in
the middle by a sort of tendinous raphe. The anterior end of
the infralabial part is inserted on the lower jaw. In the deeper,
longitudinal layer the fibres are all posteriorly longitudinal, but
the front end of the dorsal fibres are inflected and inserted into
the above mentioned raphe, while the more ventral fibres are
going to the angle of the mouth. A pars supralabialis is not
present. — Musculus nasalis and mentalis are present.

In Erinaceus (PL 16, fig. 18) the superficial layer of the buccinator
behaves in nearly the same manner as in the Dog. The
deeper, longitudinal layer is all longitudinal; the ventral parts
thereof are rather strong and extend into the lower lip. The m. nasalis
(PL 11, fig. 3) is split in several layers between which the tendons
of the maxillo-labialis are situated. The m. mentalis is present.

2*