688 ALLIS. (Vou. XII. 
the united nerves continues forward along the ventral surface of 
the obliquus ventralis primus, sends a branch from its posterior 
edge into that muscle, another inward and backward to the 
tissues of the floor of the branchial chamber between the ventral 
ends of the first and second arches, and then continues forward 
and is distributed to the tissues between the ends of the hyoid 
and first branchial arches. Terminal branches of it extend also 
to the tissues dorsal to the ventral end of the hyoid. 
8. Nervus Vagus. 
The nervus vagus (v, especially Figs. 25, 52, 53, 59, and 64, 
Pls. XXV, XXXIV, XXXV, and XXXVIII), excluding the 
nerve of the lateral line which has already been described, arises 
by several rootlets which are usually grouped in two main 
bundles, the anterior of which arises by one or two rootlets 
and the posterior always by three or more. The most posterior 
of these rootlets always arises a little behind the others and 
runs at first directly outward, or even outward and a little for- 
ward, instead of outward and backward as do the others. The 
long line of origin of the root lies about opposite to, or a little 
in front of, the inner edge of the strongly projecting ridge that 
forms the posterior wall of the labyrinth chamber. The root, 
owing to its extended line of origin, is at first flattened horizon- 
tally, but the posterior edge soon turns downward, thus twisting 
the root through about go°, and so presenting its flattened sur- 
face at first upward, backward, and inward, and then nearly back- 
ward and inward. In this twisted position it is joined by the root 
of the lateral nerve which lies along its upper, anterior edge, over- 
lapping it somewhat. The united roots then run outward and 
backward along the membranous and cartilaginous posterior 
wall of the labyrinth chamber, and issue together by the large 
vagus foramen. This foramen (vf/7, Figs. 9, 10, and 11, PI. 
X XI), as Sagemehl has stated, lies between the intercalar and 
the occipitale laterale ; but as the intercalar in Amia is a super- 
ficial bone, and probably a membrane bone, the foramen is 
properly a perforation of the anterior margin of the occipitale 
laterale, nearly inclosed in that bone, but still lying between 
it and the cartilage of the skull in front of it. 

