BRANCHIAL SENSE ORGANS IN ICHTHYOPSIDA, 99 
GENERAL SCHEMA OF THE DEVELOPMENT OF A DorsAL 
Root or A CRANIAL NERVE. 
According to the existing views of the development of a 
dorsal root of a cranial nerve in Elasmobranchii, based 
mainly on the researches of Balfour,! Marshall,? and Van 
Wijhe,® the nerve soon after its development from the neural 
ridge divides into two main branches, a dorsal one and a 
ventral one. The dorsal branch is sensory, and supplies the 
so-called organs of the lateral line. The ventral one is mainly 
motor; it soon divides again into two branches which, as 
Stannius* first showed, pass one on each side of a visceral cleft. 
The posterior branch is mainly concerned with the innervation 
of the gill muscles. According to Van Wijhe, the dorsal 
branch becomes intimately connected with the skin, and is 
there in connection with the rudiments of the so-called sense 
organs of the lateral line. He further holds that the sensory 
epithelium takes part in the formation of the nerve. In this 
respect the dorsal branch differs from the ventral one, which 
does not, according to any writer, arise either wholly or partially 
from the skin, but is a direct outgrowth of the neural crest 
(Marshall). The branch in front of the cleft is developed later 
than the other branches, but how is still uncertain. At any 
rate, both Professor Froriep and I have failed to gather from 
Van Wijhe, who alone has studied the development of this 
branch, how this branch and the Ramus pharyngeus are 
developed. In Amphibians Gétte’ long ago held that the so- 
called dorsal branches were split off from the skin. 
1 Balfour, “ Elasmobranch Fishes.” 
2 Marshall, “The Development of the Cranial Nerves in the Chick,” 
‘Quart. Journ. Micr. Sci.,? 1878; Marshall, “On the Head Cavities, &c.,” 
‘Quart. Journ. Mier. Sci.,” 1880; Marshall, “On the Segmental Value of 
the Cranial Nerves, &c,”’ ‘ Journ. of Anat. and Physiol.,’ 1882; also separate. 
3 Van Wijhe, ‘Ueber die Mesodermsegmente u. die Entwickelung der 
Nerven des Selachierkopfes,’ Amsterdam, 1882. 
* Stannius, ‘ Das Peripherische Nervensystem der Fische,’ 1849. 
5 A Gotte, ‘ Entwickelungsgesch. d. Unke,’ 1875. 
