112 JOHN BEARD. 
described by Semper, and afterwards more fully by Van Wijhe 
in Elasmobranchs. 
The point is far easier to determine here than in the cases 
of other supra-branchial nerves, indeed, it attracts the eye with 
startling distinctness in horizontal longitudinal sections of 
embryos of the proper age. The nerve is formed as the sensory 
thickening grows backwards along the body. It is well shown 
in figs.40 and 41, /. z., and can be traced from the vagus ganglion 
(vg. gl.) backwards along the thickening, gradually becoming 
thinner and less differentiated until finally it ceases in the cells 
of the sensory thickening. 
That here there is no actual growth backwards of the nerve 
is obvious enough, for when the development has taken place 
for some length, then near the ganglion the nerve is fibrillar 
and has few nuclei, these latter increasing as the nerve pro- 
ceeds backwards, and the fibres becoming pari passu, 
fewer, and ending gradually in the protoplasm of the sensory 
thickening. 
Where the compound vagus ganglion (vg. gl. 2, 3, 4) sepa- 
rates from the skin (fig. 36) it is easily seen that above each of 
the three branchial clefts, viz. the third, fourth, and fifth 
branchial clefts, fibres are given off from the separating 
ganglion to the sensory thickening. In fact, each of the 
elementary nerves making up the vagus compound, viz. vg. 2 
and 3, and the intestinal branch, vg. 4 and 5, takes part in the 
formation of the so-called “ lateral line.’ In other words, the 
lateral line is made up of supra-branchial nerves of at least 
four segmental nerves, probably of more than four, viz. vagus 
2,3, 4, and 5. The fifth root is the rudiment of the nerve of 
the rudimentary cleft mentioned before. 
We have seen that the facial, which is probably a com- 
pound nerve, has a large forked supra-branchial branch, 
and we shall find that the fifth and ciliary also, as already well 
known, have each a very long supra-branchial nerve, extending 
over the snout (fig. 51, op. s. and oph. pro.), and hence we need 
not be much surprised that a supra-branchial nerve, which is 
made up of the elements of at least four supra-branchial 
