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15 Mammals generally.

In Lemur the ordinary two layers of the m. buccinatorius
are developed. The transverse layer is very strong and all its
fibres are curved into the lips; a great posterior portion of the
fibres of the upper lip have an oblique direction and are inserted
into the maxillary bone — as is also the case with part
of the transverse layer in Halmaturus1). Posteriorly the m. buccinatorius
consists only of the longitudinal layer, extending forward
inside the transverse layer, which externally is intimately
connected with the anterior end of the platysma.

In the Rabbit (PL 16, fig. 19) there is in the buccinator a
superficial, principally transverse layer; but the fibres are partly
more or less oblique, the most anterior (a) having a direction
somewhat from above-forward to below-backwards, the next (b)
having in turn a direction from above-backward to below-forward;
the last named crossing and overlaying the former. Inside this
transverse layer there is a well-defined longitudinal layer extending
also into the upper lip. On the side of the maxilla,
dorsad to the parts described of the buccinator, is situated a
layer of transverse (vertical) fibres (c), whose ventral ends are inserted
into the buccinator; this muscular plate is evidently a separate
part of the buccinator (comp. the buccinator of Halmaturus
, where also part of the muscle extends upon the upper jaw).

In Myopotamus (PI. 14, fig. 4) the ends of most of the transverse
buccinator-fibres are not inserted into the upper and lower
jaw respectively but join the corresponding fibres of the other
side below the intermaxillary bone, and above the mandible,
behind the incisors. On the dorsal side, viz. below the intermaxillary
bone, the fibres of the right and the left buccinator pass
direct into each other. On the ventral side, above the mandible,
the muscular fibres of the right and left buccinator are very near
each other, but do not pass direct into one another; the bundles
passing into fine tendons, which go from one side to the other,
crossing each other. In this manner a powerful sphincter round
the front part of the oral cavity is formed. This sphincter is probably
developed in many other Rodents and is the active agent
in the peculiar shutting of the mouth behind the incisors as is
the case in many Rodents.

The general results of the foregoing investigation respecting
the buccinator-group in the Viviparous Mammals may be summarized
as follows (comp. PI. 17, fig. 3—4):

The buccinator-group consists of three muscles: buccinator,
nasalis and mentalis. The buccinator forms the bulk of the cheek
and extends into the upper and lower lip. The original transverse
arrangement of the bundles, still found in Echidna, has
been modified so that one may generally distinguish two distinct
— but in some points intimately connected — layers, a superficial
transverse and a deeper longitudinal layer; the anterior
bundles of the superficial layer are bent so that the ends thereof
are directed into the upper and lower lip, running parallel to
the margins of the lips, sometimes joining in front the corresponding
portion of the opposite side: pars rimana buccinatorii2);
sometimes also the deeper, longitudinal layer takes part in the
formation of this muscular portion. Within the pars rimana in
the upper lip is often developed a deeper layer of transverse
fibres, pars supralabialis buccinatorii, generally appearing as a continuation
of the longitudinal layer of the cheek. Sometimes the
buccinator presents even other complications: a third, and deepest
layer may be present; and at the lower margin of the buccinator
may be developed a special branch of the muscle extending into
the median part of the lower lip. — The nasalis and mentalis
take their origin from the upper and lower jaw respectively, near
the teeth, and extend upward-laterad and downward-laterad, ending
in the skin, the first being generally divided into several
parts separated by the tendons of the maxillo-labialis. We think
it probable, that these muscles are derivations of the buccinator.

5. MUSCULUS LATERALIS NASI.

In some of the Ungulata (Horse, Ruminants with the exception
of the Camels) a muscular fringe consisting of transverse

*) In the same manner as in the Prosimise also in the Dog and Erinaceas a
smaller posterior portion of the fibres of the upper lip are inserted into the
maxillary bone (comp. PI. 16, fig. 17 and 18; the fibres directed obliquely upward).

2) The »orbicalaris oWs« autt. is partly this muscle, partly the front portion
of the sphincter profundus (comp. p. 7).

Buccinator-group. Lateralis nasi. Recti. Ear-muscles. 16

fibres is present on the border of the soft nasal wall and the
adjoining bones (nasal, intermaxillary, maxillary) and cartilages,
the muscular fibres taking their origin from the said bones or
cartilages and extending on the soft nasal wall. Sometimes it
may be separated in two disconnected portions. This muscle is
best developed in the Horse (PI. 8, fig. 1). Also in the Dog (PL 12)
we have found traces of it at the posterior end of the lateral
face of the nasal cartilage. How far it is present in other than
the said Mammals and the Elephant (vide infra) we are at a loss
to say; we have not found this feeble muscle in others, but must
remark that we have not sought much for it, so that it is very
possible, that it is more often present than would appear to be
the case.

From the m. lateralis nasi probably may be derived some
minor muscles in this region, which run from one part of the
nasal cartilage to the other or from the cartilage to the soft nasal
wall. To these muscles, which we have not had an opportunity
of investigating more closely, belongs the m. transversus nasi of
the Horse, which is more developed than is generally the case
with these muscles; some parts of the transversus nasi of the
Horse are continued direct into the lateralis.

6. MUSCULI RECTI NASI ET LABIORUM.

In the lips, and also in the soft parts of the nasal tube,
there are in many Mammals numerous muscular fibres present,
going transversely from the skin to the mucous membrane. The
fibres are according to Perregaux1) generally present in the lips
and are here termed by Aeby m. rectus labii; in the Ungulata
which we have examined in this respect they are present. But
as already stated similar fibres may also be found in the soft
nasal tube, where we have found them in the Camel, Elk, Horse
and Tapir and where they have probably a wider distribution.
We term the lastnamed fibres m. rectus nasi2).

7. MUSCLES OF THE EXTERNAL EAR.

The muscles which are connected with the external ear we
shall treat under this head with the exception of the auricular
portion of the sphincter profundus, which has already been described
. Besides the muscles inserted into the external ear or
being situated wholly on it, we also here treat of those, which
are inserted into the scutellum, a plate of elastic cartilage situated
in many Mammals before (and above) the auricle, these muscles
naturally, as we shall see, ranking among those of the auricle itself.

A. The ear-muscles in the Placentals

with a scutellum.

Of Placentals possessing a scutellum we have particularly
examined: Dog, Babbit, Elk, Cow, Swine, Horse and Tapir.

a. Scutularis-group.

PI. 15, fig. 4—5.

From the middle line of the head, from the hind parts of
the frontal surface unto above the eye, and sometimes from the
side of the face behind and below the eye, arises a broad muscular
brim, the m. scutularis, inserting into the margin of the
scutellum, and being divided into several more or less separated
subdivisions. Often the muscle instead of taking origin from the
middle line is here continued into the corresponding muscle of
the opposite side, thus forming a transverse muscular band
across the head (Dog, PL 15, fig. 5, Babbit, Elk). From the
M. scutularis branches off a bundle, pars transiens3), which is
not inserted into the scutellum, but crossing it, is inserted into
the auricle itself (on the convex side near the anterior margin,
or into this last); some of the fibres of the pars transiens may
arise from the scutellum.

x) Einiges uber die Lippenmuskulatur d. Saugetiere. Inaug. Diss. Rem. 1884.

2) The above-mentioned mm. nasalis and mentalis often join so closely with recti-
bundles, having also a similar direction, that we may not suppress the remark, that
it is not precluded, that these muscles, which we have ranked above with the buccinator
, are in reality recti-bundles, which have at one end been attached to the bone.

3) »Oberer Einwartszieher«, adductor superior, of the Veterinarians.