7 
Mammals generally. 
Platysma-sphincter-group. 
and in the Dog (PL 12) it is even rather well developed; in both, 
the cervical part of the muscle is the strongest, the cephalic part 
not extending far forward and upward. In Myopotamus, where 
it is rather thin, it is far extended on the face, as far as the 
angle of the mouth. In Sus (PL 9) the muscle, which is rather 
bulky, is present only on the neck, extending on to the angle of 
the lower jaw; an anterior, narrow portion extends below the 
platysma and on to the inner side of this muscle, and a few 
fascicles thereof are directly continued into the sphincter pro¬ 
fundus (PL 10, fig. 3); the greater, posterior, part of the muscle, as 
usual, lies on the outer side of the platysma. In other Ungulata 
it is also restricted to the neck, not extending on to the head. 
In the Marsupials, the Prosimice and Primates, it is not present 
(at most in the Prosimise there may be traced vestiges of it). 
The sphincter profundus when most completely developed 
extends forward to the anterior extremity of the head; upward 
it extends to the eye, and the ear (PL 17, fig. 2). The hindmost 
part is inserted into the tragus of the auricle, acting as a de¬ 
pressor of the ear, portio auricularis. A middle portion of the 
muscle extends into the lower eyelid, acting as a depressor thereof: 
portio palpebralis. The part of the muscle which connects these 
two portions we term portio intermedia. Finally there is a front 
part of the muscle, the portio oris, generally termed muse, orbi¬ 
cularis oris l ). The fibres are here curved in such a manner, that 
they more or less perfectly surround the cleft of the mouth. The 
direction of the fibres in the rest of the muscle is mainly trans¬ 
verse, but in the hind part of the muscle the direction is ventrally 
more antero-posterior; and sometimes these fibres are inserted 
into the anterior end of the sternum. Ventrally the transverse 
bundles of the right and left muscle are sometimes directly con¬ 
tinued into one another, or the bundles may cross one another, 
or they may be separated in the middle line by a linea tendinea, 
or they fail to reach one another, or parts of the muscles may 
behave in one, parts in another manner in the same animal. 
A complete development of the muscle as just described is 
not found in many Mammals. The portio oris we know only in 
the Dog and the Rabbit. The portio intermedia has often been 
suppressed, the portio palpebralis and auricularis thus representing 
two distinct muscles. 
As a continuous muscular plate, extending from one end of 
the head to the other, the muscle is developed in the Dog (PL 15, 
fig. 2). The portio oris, which extends round the angulus oris into 
the upper and lower lip (but not to the anterior end thereof), pro¬ 
ceeds posteriorly in the following part of the sphincter, the fibres 
lying in the same plane and becoming gradually less curved, and 
more transverse; thus passing over into the portio palpebralis, 
which is large and intimately connected with the orbicularis 
oculi. The portio auricularis is very distinct, the portio intermedia 
being thinner and composed of more loosely connected bundles. 
In the Prosimice the sphincter profundus is a continuous 
rather well developed thin plate, but an insertion into the au¬ 
ricle does not always take place, and the portio oris is not present, 
or at most only a few fibres are continued into the upper lip 2 ). 
In the Rabbit the sphincter profundus extends as a conti¬ 
nuous plate from the anterior end of the sternum, from which 
a part of its fibres takes origin, unto the angle of the mouth. 
A powerful portio auricularis is present, but the portio palpe¬ 
bralis does not reach the orbicularis oculi. The portio oris ex¬ 
tends only into the upper lip. 
In the following forms there is no portio oris; the sphincter 
does not extend so far forward on the face. 
In Centetes (fig. C) and Halmalurus (PL 15, fig. 2) the sphincter 
profundus is well developed, and continuous; the portio auricu- 
J ) Not every muscle, which is termed »musculus orbicularis oris«, is the portio 
oris of the sphincter prof. In most Mammals the »m. orbicularis oris« is wholly, 
or in part, a portion of the buccinator (v. below). 
2 ) What Ruge (Gesichtsmusk. d. Halbaffen, in: Morph. Jahrb. 11. Bd.) terms 
the orbicularis oris (and the caninus ) in the Prosimise is the superficial transverse 
layer of m. buccinatorius, behaving in a quite similar manner as the correspon¬ 
ding part of the Dog and Hedgehog; in the figures of Ruge it appears as if his 
orbicularis oris and caninus were a direct continuation of the sphincter profun¬ 
dus — but we have not found it so. Comp, the description of the m. buccina¬ 
torius, hereafter. 
laris is connected with the ear; the portio palpebralis extends, in 
Halmaturus, generally unto the orbicularis oculi and is inserted 
into it; but in Centetes, and in one of the specimens of Halma¬ 
turus examined, it does not reach the orbicularis. In Centetes 
the bundles of the hinder part of the muscle ventrally meet 
the corresponding muscle of the other side in a tendinous line, 
whereas the bundles of the greater anterior part of the muscles 
are directly continued from one side to the other. In Myopotamus 
the muscle is very strong, the caudal end thereof being connected 
with the front end of the sternum; the hindmost part of the 
muscle, as usual, forms a fleshy portio auricularis, but further 
forward the dorsal part of the muscle is represented by an apo¬ 
neurosis, the fleshy part of the muscle being situated for the 
most part ventrally. 
In the Ungulata generally the portio intermedia has totally dis¬ 
appeared, the portio auricularis and the portio palpebralis being 
quite separated; at most a small part of the portio intermedia has 
been preserved in connection with the portio auricularis. In all 
the Artiodactyla examined by us (viz. Sus, Camelus, Alces, Cervus 
canadensis and Aristotelis, Bos) both the said portions are well 
developed. In the Elk (PL 15, fig. 6) the portio auricularis is a true 
sphincter, whose anterior bundles run as an arch from one au¬ 
ricle to the other below the neck; the hind bundles radiate like 
a fan on the underside of the neck, in the middle line crossing 
those of the other side. In Cervus Aristotelis the very well deve¬ 
loped portio auricularis is not a true sphincter, the bundles in 
the middle line being separated from those of the other side by 
a tendinous line. In this species there is a distinct remnant of 
the portio intermedia, attached to the front margin of the portio 
auricularis, extending a little on the surface of the masseter. In 
the Perissodactyla, viz. Tapir and Horse, the portio palpebralis is 
only slightly developed, in the Tapir (PL 7) being connected with 
the buccinator (PL 8, fig. 2), of which it is in this animal appa¬ 
rently a detached portion; in the Horse (PL 8, fig. 1) it is a very 
thin weak muscle, the ventral ends of whose bundles are directed 
somewhat more forward than usual; in both animals the por¬ 
tion is connected with the orbicularis oculi. The portio auricularis 
in the Tapir (PL 7) is partially a true sphincter, the hind bundles 
forming a sling from one ear to the other; in the Horse there is 
no such connection. 
In Echidna (PL 10) the muscle presents rather striking pecu¬ 
liarities. Only the hind part of it, behind the ear, is developed; 
it is in the usual manner attached to the ear-conch, but is much 
larger than the portio auricularis of other Mammals, being a power¬ 
ful muscle extending beyond the median side of the fore-limb 
and on the ventral side of the trunk, Where it is connected with 
the cutaneous muscles of the latter. A point of great interest is 
that the sphincter profundus and the sphincter superficialis in Echidna 
ventrally run into one another (PL 10, fig. 2), so that both, to 
some extent, form one muscle, with a deep cleft, in which the 
platysma has its place 1 ). This arrangement in a form such as 
Echidna makes it rather probable that the two sphincteres were 
originally one muscle: there seems to be no reason to suppose 
that the connection of the sphincter superficialis and profundus 
in Echidna is a secondary one 2 ). 
In Ornithorhynchus there is no sphincter profundus. 
The intermediary sheet of our complex is the platysma 
(PL 17, fig. 1), whose bundles have chiefly, and markedly, a longi¬ 
tudinal direction. It is always present. Primarily it is a great 
continuous muscular plate extending from the neck to the angle 
of the mouth or still further forward; occupying the side of 
the head below the eye and the ear (seldom extending above 
them). But it may be transformed in various ways: sometimes 
either the hind or the front part of the muscle has been re¬ 
duced to an aponeurosis, the front or the hind part of the 
muscle respective!)' being muscular; and instead of being conti¬ 
nuous the muscle may have been split in two or more portions, 
x ) In the individual examined an aberrant bundle from the sphincter prof, ex¬ 
tends on the outer surface of the platj^sma (a PI. 10, fig. 1—2). 
2 ) Comp, also the singular connection of some fibres of sphincter superficialis 
■with the auricular portion of sphincter profundus in Sus. (p. 7). 
