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Mammals generally.

Ear-muscles of Marsupials. Do. in Placentals without scut. Monotremes. 22

direction; the foremost portion is the largest, the hindmost the
smallest. We term them pars anterior, intermedia and posterior.
The pars anterior and intermedia represent together the m. auri-
culo-occipitalis of the Placentals. The pars anterior is fanshaped,
the muscle taking its origin from the posterior end of the sagittal
crest, from which point the fibres diverge, those near the median
line having a longitudinal direction, while those of the lateral
parts have a direction somewhat transverse. In front of the
opening of the ear-conch (fig. A) is situated a narrow muscular
slip, which is inserted into the posteron 4 near the insertion of
the auricular portion of the sphincter profundus; it evidently
corresponds to the adductor inferior of the Placentals. If we follow
the fibres of this muscular slip from their insertion we find
them going dorsad, below the terminal part of the scutularis, and
being continued into some of the above-named lateral fibres of
the anterior part of the muse, auriculo-occipitalis, while others
are inserted direct on the auricle (anteron 5). Where the fibres
of the two muscles, the scutularis and the auriculo-occipitalis,
cross one another, they are intimately connected. It is evidently
in this place that the scutellum has been developed in the Placentals
; and as a consequence of the development of the scutellum
parts of the two great muscles have been cut off respectively
to form the levator brevis (from the scutularis) and the adductor
inferior (from the auriculo-occipitalis). — The pars intermedia is
inserted into the convex surface of the auricle much as the
posterior part of the auriculo-occipitalis is inserted in the Placentals
. — The pars posterior of the muscle inserts into the auricle
in the same place as the deep portion of the postauricularis
of the Placentals and evidently corresponds to this. In what
manner the superficial portion of the postauricularis in the Placentals
has taken its origin we cannot say with certainty. In
Didelphys there is no trace of it. Possibly it has arisen from
the pars intermedia of the auriculo-occipitalis + postauricularis of
Didelphys, this portion having been split up into two layers, of
which the deeper has been developed into the superficial portion
of the postauricularis.

In Halmaturus the m. scutularis and the auriculo-occipitalis
+ postauricularis behave in the main in the same way as in Didelphys
, but the anterior part of the auriculo-occipitalis + postauricularis
has a somewhat more complicated structure.

The m. temporo-auricularis is in Didelphys quite similar to
that of the Placentals and gives no key to the understanding of
this muscle. It takes its origin from the mandible, and is inserted
into the anteron 5 and the neighbouring parts of the auricle
, below the insertion of the scutularis. — In Halmaturus (PI. 13,
fig. 3) this muscle differs in taking its origin from the hind part
of the zygoma (comp. the Placentals).

The muscles, which both arise from, and are inserted into,
the auricular cartilage, we have only studied in Halmaturus; which
possesses the same muscles as the Dog. They present no marked
features of interest.

The m. anteri sexti (PI. 13, fig. 2; comp. fig. 3) has its place
before the anteron 6, bridging the incisure which separates a
proximal spiniform part from the rest of the anteron.

The m. posted septimi (PI. 13, fig. 1—2; comp. fig. 3) is a flat
muscular band going from the proximal margin of the posteron 7
to the posteron 5 bridging the broad incisure between them.

The m. fissuralis takes its origin from the concave (hinder)
side of the anteron 5, and is inserted into the end of the posteron
4.

The m. trago-anterus arises from the proximal corner of the
anteron 5 and is inserted into the posteron 4 outside the m. fissuralis
.

C. The ear-muscles in Placentals
without a scutellum.

Among the Placentals, in which no scutellum is developed,
we have studied the ear-muscles of Centetes (fig. B, G). We onty
describe the muscles going from the head to the auricle.

Of greater ear-muscles Centetes possesses the same as other
Placentals, viz. scutularis, auriculo-occipitalis and postauricularis.
Besides these there is an adductor inferior and a temporo-auricularis
.

The scutularis (fig. G) is divided into three portions, which
appear as separate muscles, 1) an antero-superior, 2) an anteroinferior
and 3) a posterior portion. The first (a) arises on the upper
side of the skull in front of the eye, close to that of the
opposite side; only the inferior fibres thereof reach the ear (anteron
5), the superior ending free, intermingling with those of
the other portions. The second portion (c) takes its origin from
the angle of the mouth (comp. the pars antero-ventralis of the
Dog, p. 17) and goes to the ear, where some bundles of it insert
into the anteron 5, while the rest extend above the ear, the
fibres intermingling with those of the first and the third portion
(b) which latter has a transverse direction and, in the middle
line, joins the corresponding muscle of the other side, thus forming
a broad muscular band going across the skull from one
ear to the other; only the posterior bundles, corresponding to
the pars transiens, reach the auricle, the rest intermingle with
the fibres of the two other portions.

Close in front of the anteroinferior portion (c) is situated a
muscle (d) taking its origin from the small zygoma below the
eye, and ending, halfway between the eye and the ear. We suppose
that this muscle is a detacted part of the anteroinferior
portion of the scutularis.

The auriculo-occipitalis (fig. C) is a large, thin, muscular plate
which takes its origin from a long tendinous stripe on the occiput
and the neck and only at its antero-external angle is inserted
into the auricle, while for the rest, it covers the dorsal
side of the head between the auricles, and further forward.

The postauricularis (fig. C) consists of a superficial part composed
of two deeply separated slips, and of a deep portion,
represented by a long slender muscular ribbon.

The adductor inferior (fig. B) arises on the face, in front of
the ear, and extends backward inserting into the base of the
tragus.

The temporo-auricularis takes its origin from the mandible
and is inserted into the anteron 5.

Of the ear-muscles of Centetes the scutularis is of special
interest. We suppose, that Centetes is to be derived from a Mammal
which possessed a scutellum, in other words, that the absence
of this has not as in the Marsupials a primitive character.
The several portions into which the scutularis is separated we
think is an indication of the original presence of a scutellum,
lying in the place where the greater part of the fibres of the
three portions meet one another. The connection of the scutularis
with the auricle we regard as secondary (that of the pars transiens
naturally excepted).

In a similar manner we think that the ear-muscles of other
Placentals lacking a scutellum should be interpreted. But we
have not been able to spare time for making further investigations.

D. The ear-muscles of the
Monotremata.

We regret to say, that the Monotremata, of which we have
examined Echidna (PI. 10), do not afford decisive contributions
to the understanding of the ear-muscles.

The rather large ear-cartilage of Echidna is almost wholly
imbedded in the large muscular mass of the platysma. An insertion
into the auricle takes place only to a very limited extent.
On the mediad side there is inserted a well-defined bundle of
the platysma. This having a dorso-ventrad direction, perhaps, is
the homologue of the terminal slip of the scutularis in Didelphys.
Another slip, having a direction from behind forward, is inserted
into the hinder side of the tragus, into which is also inserted a
small portion of platysma taking its origin from the anterior
margin and the adjoining part of the concave side of the auricle
(b, PL 10, fig. 1); and of the platysma-bundles which go to
the angle of the mouth the deeper ones take their origin from
the tragus; whereas the superficial ones come from the bulk of

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