9 
Mammals generally. 
Platysma-sphincter- and Orbicularis-oculi-group. 
10 
one of which appears as the principal platysma. The platysma 
may be a pure cutaneous muscle, but sometimes parts of it are 
connected with certain of the underlying bones. 
In Echidna (PL 10) the muscle is more powerfully developed 
than in anj r other Mammal; extending not only under the ear 
and the e}re, but also above the ear, where it meets the correspon¬ 
ding muscle of the other side, and posteriorly being continued into 
the cutaneous muscle of the back of the trunk. The part of the 
muscle lying above and behind the external ear is very thick 
and studded with the deep follicles of the spines of that part of 
the body. Most of the bundles have the usual, longitudinal di¬ 
rection, but in the part of the muscle which is placed before 
the auricle the bundles have a more oblique direction. The post- 
auricular part of the muscle is continued below the ear into a 
rather narrow band, which extends forward and is inserted on 
the superior maxilla below the eye. The praeauricular portion 
of the muscle extends below the eye and is here, ventrally, inti¬ 
mately connected with the postauricular portion and also inserted 
on the superior maxilla; dorsally and in front, it is intimately 
connected with, or rather continued into the orbicularis oculi 
(comp, below). 
In Ornithorhynchus also the platysma forms a large muscular 
plate extending from the fore-limb to the angle of the mouth, 
but the greater part of the muscle here lies below the ear-ope¬ 
ning. The lower parts of the muscle end in the skin ventrally, 
the upper parts are inserted on the maxillary bone. The part of 
the muscle lying between the eye and the ear (which two are 
only separated by a very short distance) is very small. 
In Halmaturus (PI. 13, fig. 1) the platysma is a continuous, 
strong, muscular plate; extending from the neck to the angle of 
the mouth, reaching dorsally very nearly to the external ear. 
In Didelphys (fig. A), Centetes (fig. B) and the Dog (PI. 12) the 
muscle is similarly developed as a strong muscular plate, exten¬ 
ding from the neck, below the ear, to the angle of the mouth. — 
In Myopotamns, in which the platysma is still a continuous mus¬ 
cle, the muscular fibres only extend a short way upon the head 
(on the hind part of masseter), the front part of the muscle being 
represented by an aponeurosis extending further upon the face; 
the hind part of the muscle, lying on the neck, forms a rather 
strong muscular plate. 
In the Ungulata (PI. 5, 7, 9) the dorsal part of the platysma 
has generally been separated from the major part of the muscle 
as a fleshy band, which takes its origin from the zygoma, and 
runs to the angle of the mouth. We term it the pars zygomatica 
platysmatis (muse, zygomaticus autt.). In Alces the pars zygomatica 
and the rest of the platysma, pars principalis, at the fore-end, 
near the angle of the mouth, to the extent of a couple of cm, 
are closely united, so that it is impossible to point out any limit 
between them; the fibres of the pars principalis, which is a 
rather narrow band on the lower part of the side of the head, 
have a longitudinal direction. In all other Ungulata examined by 
us the pars zygomatica and the pars principalis are separated 
throughout their whole extent. In the Camel (PI. 5) the fibres of 
the pars zygomatica have the same direction as in the pars prin¬ 
cipalis (which is a broad band of longitudinal fibres) and the 
front ends of both are inserted into the buccinatorius. In both 
the hind end of the muscle is represented by an aponeurosis, that 
of the pars zygomatica connected with the zygoma, and that of 
the pars principalis extending from the angulus mandibulte round 
the neck. But in most Ungulata the direction of the fibres in the 
two parts is not quite the same and they may cross each other 
under obtuse angles (Tapir, PI. 7, etc.) and behave as muscles 
which have nothing to do with each other. In Sus (PI. 9) the 
upper part of the pars principalis spreads like a fan on the face, 
below and behind the eye: and this feature is still more marked 
in some of the Ruminants; for instance Bos, where this part of 
the muscle is dissolved into a number of disconnected thin and 
narrow muscular bands spreading over the face. 
In the Primates there is, as is well known, a muscle very 
similar to that which we have termed the pars zygomatica pla¬ 
tysmatis in Ungulata. This muscle — musculus zygomaticus — 
has, according to Ruge 1 ), been derived from the m. auriculo- 
labialis superior of the Prosimise, and we think he is quite right 
in this. The m. auriculo-labialis sup. of the Prosimise is our m. 
postorbicularis. As we must derive our pars zygomatica in the 
Ungulata from the platysma, it is probable that it has been 
developed from other elements than the similar muscle in Pri¬ 
mates. As we shall see later on, some muscles which in various 
other Mammals have been termed »musculus zygomaticus« have 
also an independent origin. 
2. ORBICULARIS-OCULI-GROUP. 
The group of muscles, which we term the orbicularis-oculi- 
group (P. 17, fig. 1; PI. 16, fig. 20—27) consists firstly of the well- 
known muscle surrounding the opening between the eye-lids: 
secondly of several other muscles, which evidently are derived 
from the orbicularis. The orbicularis itself has, as is also insisted 
on by Ruge, probably been derived from the platysma, to the 
dorsal margin of which its ventral part fits in in such a manner 
in Echidna, that it has quite the appearance of their being of 
one set. 
As to the orbicularis proper; the fibres composing it in the 
forms which we have examined, generally do not wholly encircle 
the palpebral fissure. In the Ungulata, which we have prin¬ 
cipally studied in this connection, they are always interrupted 
at the front angle of the eye by the front palpebral ligament. 
Sometimes, as in the Horse (PI. 16, fig. 26), the fibres with this 
exception go all round the eye; but generally a number of them 
have a more limited extension: 1) some only lying in the upper 
lid cross others only lying in the lower lid at the posterior 
angle of the eye (Camel, PI. 16, fig. 21); 2) fibres lying prin¬ 
cipally in the upper lid go from this round the posterior angle 
into the lower lid but not wholly round to the anterior canthus 
(Zebu, Wapiti, fig. 23—24); 3) fibres lying principally in the lower 
lid go round the posterior canthus into the hind part of the su¬ 
perior eyelid (Alces, fig. 22); 4) some fibres go from the anterior 
canthus only a short way into the lower (fig. 23—24), resp. the 
upper eyelid; 5) some fibres only encircle the posterior angle of 
the eye (fig. 27). 
From such incompletely developed parts of the orbicularis- 
fibres the annexed muscles of the group are derived. From fibres 
encircling only the posterior angle of the eye (5) is derived the 
musculus postorbicularis, a muscular plate whose fibres some¬ 
times have a similar direction to those of the orbicularis proper 
(Tapir, PI. 16, fig. 27), but generally have taken a more transverse 
(dorso-ventrad) direction. The muscle is in some Mammals of 
considerable size, sometimes being very broad as in the Didelphys 
figured (fig. A), in others being far extended dorsad and ventrad 
as in Centetes (fig. B). Sometimes the fibres have been divided 
transversely (Horse, PI. 16, fig. 26), the muscle being thus sepa¬ 
rated into a dorsal and a ventral portion. 
In Bos, Alces (PL 16, fig. 22), Wapiti (fig. 24), Dog (PL 12) at 
the hind angle of the eye there lies a little narrow flat muscle, 
m. horizontalis nob., consisting of longitudinal fibres, taking its 
origin in the fascia of the m. temporalis. As to the homology of 
this muscle w r e waver. The muscle has much the appearance of 
an intruder into the orbicularis-group, belonging to quite another 
system than the rest of the orbicularis, and we have for a time 
been inclined to think, that it was a detached piece of muscle be¬ 
longing originally to the scutularis- group. But the superficial posi¬ 
tion of it goes against this supposition, the scutularis lying always 
inside the postorbicularis, if extending into the part of the face 
occupied by this muscle; while the m. horizontalis lies outside the 
postorbicularis. Perhaps the horizontalis consists of orbicularis- 
fibres which have taken a deviating direction; sometimes (comp, 
the upper fibres in the diagram of the Wapiti, PL 16, fig. 24) some 
of the fibres have a direction, reminding one somewhat of that 
of the orbicularis-fibres, which might support this supposition. 
At the anterior canthus, parts of the orbicularis, in a similar 
but more complicated manner than at the posterior canthus, have 
formed annexed muscles. In Echidna (PL 10, fig. 1), fibres lying 
before and intimately connected with the orbicularis proper form 
a flat muscle in front of the eye: m. prceorbicularis; the fibres are 
l ) Gesichtsmuskulalur d. Priraaten. Leipzig 1887. p. 61. 
