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Mammals generally.

Orbicularis-oculi-group. M. maxillo-labialis.

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principally transverse, but at the upper end they expand like a
fan, the posterior fibres extending above the eye. In the other
Mammals which have been closer examined the muscle was
found to have become separated into several muscles.

Firstly most of the fibres in front of the eye have been divided
transversely by the anterior palpebral ligament; the prse-
orbicularis being thus separated into a prceorbicularis dorsalis and
uentralis; sometimes however some bundles go from one into the
other (Horse, PI. 16, fig. 26). From the palpebral ligament the
fibres of these muscles extend respectively dorsad and ventrad,
close to the orbicularis proper, being a direct continuation of
this; the fibres having principally a transverse direction, generally
spreading like a fan respectively dorsally and ventrally.
Posteriorly the prseorbicularis dorsalis may be continued into a
m. supraorbicularis, which sometimes (Elk, Camel, Swine, PI. 16,
fig. 22, 21, 25) is a direct caudad continuation of the prseorbicu-
laris dorsalis; the fibres have a similar direction like the posterior
fibres of the prseorbicularis dorsalis, viz. oblique, the lower ends,
which are attached to the orbicularis, being foremost. In other
cases the supraorbicularis has been more completely differentiated
from the rest of the prseorbicularis dorsalis; in the Horse (PI. 16,
fig. 26) for instance it has become rather sharply separated, and
in the Tapir (fig. 27) it has become displaced so as to take place
inside the prseorbicularis. The same is also the case in Bos (fig. 23),
where the supraorbicularis has assumed an extraordinary development
, extending backward over the whole frontal plane, the direction
of the fibres posteriorly being longitudinal.

The prceorbicularis uentralis is in some forms feebly developed
(Didelphys, Gentetes, fig. A, B), in others it is a rather large
muscle (e. g. Bos, PI. 16, fig. 23). In Alces (fig. 22) it is very large
and divided into two portions, a hind portion (prv 2) behaving
as usual, and a front portion (prv 1) arising from the lacrymal
bone and extending downwards like a fan; it is covered partially
by the first-named portion, with which it is intimately connected.

From the prseorbicularis is also derived the m. nasolabialis
(PI. 17, fig. 1). In Echidna it is not yet separate from the prseorbicularis
, with which it is also intimately connected in several
of the others. The fibres of this muscle have generally an oblique
direction, the ventral ends, which extend into the upper lip and
unto the nares, being foremost. Originally (Didelphys, fig. A; Gentetes
, fig. B; Prosimise) the muscle extends a way above the eye;
and in Centetes this is so far exaggerated, that the muscle extends
posteriorly above the ear and further on (this is probably
a consequence of the existence of the spinous coat of this animal
). But often, as is the case with all the Ungulata examined,
the part of the muscle extending above the eye is very little developed
. The nasolabialis is generally a muscle of considerable
strength, extending often over a large part of the face. In some
forms, e. g. the Camel (PI. 5), there is no limit whatever between
the nasolabialis and the prseorbicularis, the former being a direct
rostrad continuation of the latter, especially of the prseorbicularis
ventralis; in other forms, as the Tapir (PL 16, fig. 27; PI. 7), it is
more, but not quite, independent, the caudal fibres still being
closely attached to the front margin of the prseorbicularis ventralis
. In the Horse (PI. 16, fig. 26) it is still more independent,
and in the Swine (PI. 9) it has been widely separated from the
prseorbicularis through a broad space. — The Elk presents the
peculiarity, that the right and the left nasolabialis unite above
the snout and here form a layer of transverse fibres.

The Wapiti (PI. 16, fig. 24) and the Zebu (fig. 23) are peculiar
in that a smaller or greater number of the dorsal ends of the
fibres of the prseorbicularis dorsalis turn in a bow, into the
nasolabialis, and are continued in the same direction as the
fibres of the nasolabialis, forming a smaller or greater part of
this muscle. The arrangement is such, that if no other Mammals
were known than the Wapiti and Zebu the natural inference of
the facts would be, that the nasolabialis had been derived from
the prseorbicularis dorsalis in such a manner, that the rostral
fibres of the latter had grown down in a bow into the upper
lip — an inference which the comparison with other Mammals
shows to be erroneous.

Generally, the muscle has no definite origin from the bones
of the face. But in Nasua (PI. 11, fig. 2) where the inferior ends

thereof are inserted into the tendons of m. maxillo-labialis, and
into this muscle itself, it takes a definite origin from the skull
in front of the eye, and is here intimately attached to the bone.
That it has been developed in this manner in Nasua is probably
a consequence of the development of a moveable proboscis in
Nasua; the m. nasolabialis has assumed the part of an auxiliary
of the m. maxillo-labialis — the principal motor of the proboscis —
and must therefore have a fixed origin. In the Dog, where the
inferior ends of the nasolabialis are also inserted into the maxillo
-labialis, it does not take its origin from the bone but extends
in the usual manner in front of the eye loosely connected with
the underlying parts.

3. MUSCULUS MAXILLO-LABIALIS.

The m. maxillo-labialis (PI. 17, fig. 3), which is covered by
the nasolabialis, appears as quite independent from this and
from the other facial muscles; the connection with the »caninus-
orbicularis« (front part of sphincter prof.), which Ruge has found
in the Prosimise, we have not found in the forms examined by
us, and we can only regard that connection in the Prosimise as
a quite secondary. The muscle takes its origin below, behind
and above the foramen infraorbital and extends into the upper
lip and round the external nares. The direction of its fibres is
mainly a horizontal one. At the origin the muscle is generally
fleshy, but it may sometimes arise with shorter or longer tendinous
parts. At the other end it generally terminates in several
tendons, but parts of it may also terminate fleshy.

The muscle has a distinct tendency to separate into several
portions. More especially we find a very general tendency for
this muscle to split into an upper part — the portio superior
nobis — and a lower part — the portio inferior. In Alces (PI. 11, fig. 1)
the portio superior is still coherent with the rest of the muscle, but
the fibres and tendon thereof have another direction than the rest,
which direction is oblique, and upward; the numerous branches
in which its tendon is ultimately split up, end on the upper side
of the nose. In the Horse (PI. 8, fig. 1) and the Tapir (PI. 8, fig. 2)
the portio superior (the m. levator labii superioris proprius of
the Veterinarians) has been entirely separated from the rest
through a large interstice, and ultimately it is united with that
of the other side and ends at the front end of the proboscis (in
the Tapir) or in the upper lip (Horse). — In the Camel (PI. 11,
fig. 4) the portio superior has quite disappeared, the maxillo-labialis
consisting only of the bundles arising below the foramen
infraorbital (comp. the figure of the Camel and those of the Tapir
and the Horse).

The relation of the maxillo-labialis of Centetes to that of
Erinaceus is similar to that of the same muscle in Alces on one
side and in the Horse on the other. In Gentetes (fig. G) the portio
superior is still united with the rest, but on the way to separation
. In Erinaceus (PI. 11, fig. 3) the portio superior is quite
separate (but still borders on the portio inferior) and very large,
arising from the front margin of the orbit, above and below the
entrance to the lacrymal canal; its long tendon joins — as is
also the case with Centetes — that of the other side above the
nasal cartilage and the common tendon is inserted into the skin
of the dorsal side of the tip of the nose. The portio inferior
arises in Erinaceus from the zygoma and is divided into four
parts which are rather deeply separated. The three superior are
each continued into a long tendon, which, as the corresponding
tendons in Centetes, end in the skin on the side of the nose;
the fourth, the inferior, ends fleshy in the upper lip.

In the Dog (PI. 12) there is also an upper and a lower portion
, which are quite separated throughout their whole extent;
they both arise contiguously below (and behind) the foramen
infraorbitale; into the upper margin of the lower portion the inferior
ends of the m. nasolabialis are inserted. Towards its anterior
end the upper portion is split up into numerous fine tendons
terminating behind the external nares, while the anterior
ends of the lower portion are fleshy throughout. — In Nasua
(PI. 11, fig. 2) the muscle is far stronger than in the Dog, and its