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Digital Archive of Toyo Bunko Rare Books

Not to go into anatomical details, this difference is shown, before all, in the
significant enlargement and bipartition of the musculus retrahens auris brevis, which
Kirsten aptly calls musculus abductor auris brevis. Strikingly enlarged, too,
in the ass are the musculus abductor (retrahens) auris longus; musculus adductor
(scutulo auricularis) auris inferior; musculi levatores auris longi, medius, et brevis,
and others. In consequence of the insertion, direct or indirect, of these muscles
on the occipital crista and the linea nuchalis of the occiput, it is clear that in the
ass a stronger pull is exerted on the occipital surface and the lever-arm which
is formed by the crista. Through this action there must necessarily follow an
inequality in the back part of the brain-skull.

Variations may of course be caused by the size of the ears, as also by the
manner of carrying them, as the flap-ears of the Sudanese domestic ass, in contrast
with the Asiatic. In my opinion, therefore, the most important characteristic
in the bony head for determining the specific difference between the ass and horse
is the position of the occiput. This can be recognized by three different methods
which are, however, of unequal uniformity and exactness in practice. (1) Lesbre's
method of the cheek-crista line, for the clearer expression of which I would make
a suggestion later. (2) The Frank-Nehring method—distance from foramen occip-
itale to vomer palatinum. (3) The inclination of the occipital plane mentioned by
Dugès, for the determination of which I would also propose a new method.

Besides this there are other, mostly less regularly marked, features which
can be traced to the action of the ear-musculature; the lateral edges of the occip-
italia lateralia are drawn more strongly towards the meatus auditorius externus;
the funnel of the meatus auditorius externus is more erect, etc. But, as was said
before, there is here much room for the play of individual variation.

It may occur in practice that one has only a skull of an equid without cheek-
bones or maxillæ; in this case, to determine the inclination of the occiput, use a
tangent, B, on the facies-surface of the frontales and nasales. If, on the other hand,
the maxillary is present, draw first Lesbre's line; on this (A) or on the facial tan-
gent (B) erect a perpendicular which touches the highest or most aboral point
of the crista occipitalis, and draw a tangent from this same point, first, on the
upper edge of the foramen magnum, and second, on the most aboral point of the
condyli; we find, according to my measurements of these angles to date, on thirty-
two skulls:

A 1. A 2. B 1. B 2.
Horses .............. 14-25° 10-31° 15-30° 10-25°
Asses............... 35-50° 30-35° 33-50° 30-45°

As is clear in this table, as great as is the difference between the ass and
horse, the difference between the two relations A and B is small, and we can
therefore use either the line A or B, according to the state of preservation of the
material. I call this angle ear-load index (Ohrbelastungsindex) to indicate its
dependence on the ear-musculature.

In order to express the Lesbre line numerically in an index I have applied
the following method: draw the Lesbre line and then a connecting line between
the crista occipitalis and the intersection of the Lesbre line with the articular