198 
MASARU NAGAO 
As to point three: Spec (1890) stated that the curve of Spec is found 
in those classes of mammals in which the tuberculimi articulare is 
present, and that in the same animals the antero-posterior move- 
ment of the lower jaw is possible. As examples Spec gives the names 
of the following animals: horse, Cervus elephas, Cervus dama, small 
monkeys and man. To these I can add the names of the following 
animals: Simla satyrus, Camelus bactrianus, and Lama huanacho. 
Whether or not the antero-posterior movement of the lower jaw is 
possible for these animals, I am unable to state from my own investi- 
gation. Studies have been published in regard to this question in 
some of these animals, by others, however. Descriptions of the 
movement of the lower jaw during mastication have been given by 
Meyer (1865) and by Krabbe (1892). The most entensive observa- 
tions on this subject are found in the laborious and exhaustive work of 
Lubosch (1907). The following account is based on the work of 
Lubosch, unless otherwise stated. 
It will be advantageous to discuss the motion of the lower jaw in 
terms of the following three movements; opening, lateral and antero- 
posterior movements. In marsupialia and carmvora, the lower jaw 
performs mastication principally by the opening movement (especially 
the hinge movement) supplemented by a little lateral movement. 
In penssodaciyla, besides the opening movement, both the antero- 
posterior movement and the lateral movement occur, the former 
however being much greater than the latter. In most artwdactyla, 
besides the opening, the movement of the lower jaw is principally 
lateral, although in some, e.g. pig and hippopotamus, the principal 
movement is antero-posterior with a little lateral movement. In 
rodentta, besides the opening movement, the principal movement is 
antero-posterior. 
The description of the movements of the lower jaw just given re- 
veals at once the fact that, despite the lack of antero-posterior move- 
ment during mastication, the curve of Spec is present in most of the 
artiodactyla (Lama huanacho, Rangifer tarandus, Camelus bactri- 
anus, etc.) and in the marsupialia (opossum). Furthermore, in the 
pig, guinea-pig, and rodent, in which the movement of the lower jaw 
is principally antero-posterior, the Une drawn touching the summits 
of the cusps of the bicuspids and molars does not represent the curve 
