BRANCHIAL SENSE ORGANS IN ICHTHYOPSIDA. 105 
and the pharyngeal. The development of the pharyngeal 
branch has not yet been traced. The other branches are split 
off from the epiblast. The supra-branchial (figs. 21 and 22) 
is formed at the expense of the deeper portion of the sensory 
thickening, which has begun to grow forwards over the face. 
Very soon this nerve divides into two branches; 
that is, the sensory thickening grows forwards as two divergent 
thickenings, and from each nerve-fibres are split off, and thus 
two branches are formed (fig. 51, p. b. n.). This development 
from the dichotomously dividing rudiment has been described 
by Van Wijhe.t| These two branches have been described by 
Marshall and Spencer.” The upper one is the portio facialis of 
the oph. superficialis (Marshall), the lower one the ramus buc- 
calis (Marshall and Spencer). The upper one Balfour, Mar- 
shall, and Spencer classed as a ramus dorsalis of the seventh. 
As stated by Van Wijhe,® they are concerned in the innerva- 
tion of the supra- and infra-orbital sense organs respectively 
(branchial sense organs). These branchial sense organs, it is 
hardly necessary to state, being developed from the dichoto- 
mously dividing sensory thickening mentioned above. 
The portio facialis of the ophth. superficial. (fig. 51, p. f.), 
is obviously enough, as pointed out by Marshall, Balfour, and 
- Van Wijhe, a so-called dorsal branch; that is, what we have 
here called a supra-branchial. Van Wijhe has, and I fully 
agree with him, classed the r. buccalis (fig. 51, r. 5.) as 
a “dorsal branch,” and gives these reasons: (1) Its origin 
from the same rudiment as the former nerve; (2) its 
simultaneous appearance with that nerve; (3) its similar 
development and innervation of (branchial) sense organs. 
Van Wijhe, indeed, regards the two as branches of one 
nerve, and as therefore equivalent to one so-called dorsal 
branch. Dohrn‘ has advanced very weighty reasons for the 
1 Van Wijhe, op. cit., pp. 26, 27. 
? Marshall and Spencer, ‘‘On the Cranial Nerves of Scyllium,” ‘ Quart. 
Journ. of Mier. Sci.,’ 1881. 
Op. cit., p. 27. 
* Dohrn, “Studien zur Urgeschichte des Wirbelthier-Kérpers,” No. vii, 
* Mittheil. a. d. Zool. Stat. zu Neapel,’ vol. vi, part i. 
