GANGLIA AND NERVES OF SQUALUS 45 
26. RAMUS SUPRATEMPORALIS VAGI 
The ramus supratemporalis X (figs. 1 and 7, R.St.X) arises 
near the middle of the lateral surface of the ganglion laterale X, 
from a prominent mass of cells that extends from the ganglion 
nearly to the ectoderm. Immediately after its origin the ramus 
divides into two twigs, posterior and anterior, the posterior 
nerve running nearly directly caudad and the anterior larger 
twig curving dorsal and cephalad. The anterior twig innervates 
the primordia of two lateral line organs, of which the proximal 
one (fig. 1, L.2) lies directly over the point of origin of the com- 
bined ramus and at the dorso-ventral level of the attachment 
of the roots of X to the medulla. The other organ (fig. 1, L.1) 
lies farther dorsal and anterior at the level of the entrance of 
the second root of X and at a dorso-ventral level of the dorsal 
border of the auditory vesicle. The posterior twig supplies a 
long primordium of lateral line organs (fig. 1, 1.3), to which it 
gives off two twigs, indicating that there will be at least two 
organs derived from this primordium in the adult. This lat- 
eral line primordium lies directly over the visceral ganglion of 
branchialis X, and just ventral to the level of the posterior 
roots of X. It is placed diagonally to the long axis of the body 
with the anterior end more dorsal. . 
In a 20 mm. embryo this primordium and the more posterior 
of the two innervated by the anterior twig are continuous, while 
the most anterior lateral line primordium is not present. The 
rapid appearance of these primordia at this time renders diffi- 
cult the exact identification of the organs as belonging to the 
main head lateral line or as being accessory. The occipital 
lateral line commissure is not yet formed and these organs, in- 
cluding the one innervated by supratemporalis IX, are identi- 
fied as the last four organs of the head posterior to the junction 
of infraorbital and supraorbital lines, the primordium inner- 
vated by the most proximal and posterior twig of dorsal lateralis 
VII being considered as the point of future junction of supra- 
orbital and infraorbital lines. The primordium innervated by 
