r89r.] Recent Studies of the Vertebrate Head. 99 
The neural ridge arises as a cell-growth from the closing portion 
of the neural tube, as Rabl says. Neither His’s “Zwischenstrang” 
nor Beard’s ectodermal ganglion-anlage theory is tenable. The cells 
of the neural ridge, that do not form ganglia, atrophy. The neural 
ridge may thus be regarded as merely the forerunner of the ganglia. 
The gaps between the Anlagen of the V., VII-VIII., and IX. 
nerves do not prove the absence of a continuous neural ridge in 
that region, but rather are points of atrophy. Rabl is correct in 
saying that a nerve-strand arises at the cephalic border of the 
neural ridge. The cell-mass from which this springs is anterior 
to the ciliary and gasserian ganglion Anlagen. In Torpedo a true 
ganglion is found derived from this cell-mass, but it later loses 
connection with the neural tube and neural ridge. After isolation 
nerve-fibres grow out from this ganglion, thus proving that 
sensory nerve-fibres and sensory root-fibres arise not from the 
neural tube, but from the cranial and spinal ganglia. The fibres 
of this isolated ganglion enter into such close relation with the 
trochlear nerve as to appear to belong to it. This ganglion and 
its outgrowth of fibres appear to represent the nerve ophthalmicus 
superficialis minor. The III. nerve arises by 3-7 roots from the 
base of the midbrain, and no medullary cells pass out with it. 
The ganglion, which seems to belong to this nerve, is really 
derived from the ciliary ganglion. The III. and IV. do not have 
their origin in the cephalic portion of the neural ridge. The VLE; 
as well as the III., spring from the anterior column of the medulla 
oblongata. It arises by 4—6 roots. The hypoglossus is in no 
way connected with the vagus. It is to be regarded as formed 
from the ventral roots of one or more spinal nerves, as Balfour 
thought. Van Wijhe found extending over the eighth and ninth 
myotomes an outgrowth of the neural ridge, interpreted by him 
as representing rudimentary ganglia of the second and third 
hypoglossal roots. Froriep first established the existence of 
rudimentary ganglia of the hypoglossus. Ostroumoff finds in 
Pristiurus two spinal ganglia answering to the last two roots of 
the hypoglossus. Dohrn states that the hypoglossus has as 
many ganglio Anlagen as there are ventral roots, the first being 
merely a thickening of the neural ridge. It is impossible to 
