408 THE HORSE OF ANAU IN ITS VARIOUS RELATIONS. 
Not to go into anatomical details, this difference is shown, before all, in the 
significant enlargement and bipartition of the musculus retrahens aurts 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 
Duges, 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 occipi- 
talia lateralia are drawn more strongly towards the meatus auditoritus 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 maxtlle; in this case, to determine the inclination of the occiput, use a 
tangent, B, on the faczes-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: 
re Aa. Bd; Bi2t 
HLOTSeS Scan eeet ee 14-25° 10-24° 15-30° 10-25° 
ASSES Sasa nit cetera aevere 35-50° 30-35° 35-50> 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 
