Freiburger historische Bestände - digital

G.

THE MAXILLARY MUSCLES

AND FRAGMENTS OF A DESCRIPTION OF THE MUSCLES OF THE CRANIAL PART OF THE NECK.

A. THE MAXILLARY MUSCLES.

PI. 2 and 3 (First Part), PI. 39 figs. 1—3.

The maxillary muscles of the Elephant have only been studied
by us in the specimen (no. 2), which we received in 1899, and
partially in a fragment of another head, that we received later
on from a colleague.

The masseter in Mammals generally consists of two portions,
a superficial and a deep one. These two portions, which are otherwise
inferiorly united, in the Elephant are represented by two quite
separated muscles, that have no connection at all with one another.

The masseter superficialis is laterally on its upper anterior
part covered by an aponeurosis, the extent of which is seen
in Plate 2 (of The First Part) and the bundles of which have a
direction from before backwards (and a little downwards). This
tendinous leaf has in reality a larger extent backwards than the
figure shows, a thin layer of muscular fascicles extending over it
and taking their origin from it; if these muscular bundles are
scraped off, the aponeurose becomes a larger extent. The last named
muscular bundles have a nearly vertical direction, while the fascicles
of the rest of the masseter superficialis have the same direction
as the fibres of the tendinous leaf. The aponeurosis has its
greatest thickness in front and above, and at the anterior margin
of the muscle it is thickened to a short tendinous string. The
greater part of the muscular fascicles of masseter superficialis has
its origin from the inner side of the aponeurosis. On the inner side
of the muscle lies a thin layer of muscular fascicles, which is not
sharply separated from the rest; these fascicles arise partly from
a number of thin tendons (near the anterior margin of the muscle),
partly from two thin weak tendinous leaves; the direction of these
muscular fascicles is essentially from above downwards; partially
they intercross obliquely.

The origin of the masseter superficialis is from the inferior
margin of the zygomatic arch, from the anterior two thirds of it;
the foremost end of the origin is close behind the eye. The origin
is partly and mainly through the exterior aponeurosis, described
above, partly through the interior weak tendons and tendinous
leaves (cf. above), but partly it is directly fleshy.

The insertion is on a large plane behind, below and partly
also in front of the large, rather deep depression on the lateral
side of the ramus of the mandible, down to the inferior and
posterior margin of this bone. The insertion is mostly fleshy;
only on a few points tendinous tracts are seen.

The masseter profundus takes its origin from the medial side
of about the posterior two thirds of the zygoma, at the posterior
end also from the inferior border, while in front the muscle only

arises from the upper part of the medial side of the zygoma. The
muscle is nearly a square plate, being however somewhat narrower
downwards; the distance from the anterior to the posterior margin
is somewhat greater than that from the superior to the inferior end.
The direction of the fascicles is nearly perpendicular. The muscle
is mainly fleshy; inferiorly a number of tendinous tracts have however
developed, and a few also at the top. Through a perpendicular
fissure the muscle is split into two portions, an anterior
broader and a posterior narrower (but thicker), which are connected
inferiorly. The posterior portion is inserted into the superior
part of the depression on the lateral side of the ramus, the
anterior portion in front of it on the proc. coronoideus.

Between the two masseters there is a considerable layer of
fat, which also fills the inferior part of the depression on the
lateral side of the mandible.

The m. temporalis is a powerful muscular body, filling-up
the deeply excavated fossa temporalis. Evidently it plays the principal
part among the muscles, that move the mandible; on the
specimen examined the temporalis had a weight of 2008 g, whilst
the masseter externus weighed only 436 g, the masseter internus
141 g. The muscle is certainly broadest at the top, but does not
narrow very much downwards. If we look at the muscle from
the outer side, when the mandible is in situ, we get the impression
that it is distinctly pointed towards the inferior end (First Part,
Plate 3). But in reality a considerable share of the inferior part
of the muscle is covered by the coronoid process, on the medial
side of which it is inserted (PI. 39 fig. 1).

The lateral limitation of the muscle is above and posteriorly
a thin tendinous sheet; farther down and in the front the muscular
fascicles appear; the inferior part has again a tendinous
surface (PI. 3).

The muscle arises from nearly the whole surface of the fossa
temporalis. The area of origin extends from the upper border of
the fossa until the crista orbitalis (p. 92); the lowest point of
origin is a small rough area on the squamosum, close behind
the exit of the first and second branch of trigeminus. Between this
point and the posterior root of the zygoma there is a smooth surface
, where no part of the muscle takes its origin.

The insertion of the muscle covers the whole anterior margin
of the ramus of the mandible, to where it is connected with
the body of the jaw, but further — and this is the main point
— the medial side of the ramus unto the thickened part of
the mandible enclosing the growing molars. On the other hand
the insertion only extends very little on the lateral surface (anteriorly
).