Frederic T. Lewis 213 
enters the medulla, but possesses no distinct ganglion other than the 
ganglion petrosum. Just beyond the ganglion a very slender branch, 
not drawn in the figure, passes upward and forward over the second 
cleft. This is Jacobson’s nerve. The main stem passes down behind 
the cleft where it is seen dividing into the lingual branch which extends 
forward into the hyoid arch, and a smaller pharyngeal branch which 
remains in the third arch. Notwithstanding the changed relations to 
the second cleft (such as has occurred in the seventh nerve) the lingual 
branch is presumably comparable with the prae-trematic and the 
pharyngeal with the post-trematic of fishes. In this embryo there was 
no connection between the ninth and tenth nerves. 
The tenth nerve arises from the large jugular ganglion, extending 
from which is a beaded commissure ending in a small knob. In the 
track of the commissure, but separated from it, and lying beyond it, is 
an irregular ganghonic mass. After another interval there appears a 
small fragment, and then follows the first cervical ganglion notably 
smaller and more dorsally placed than those which succeed it. The 
irregular ganglionic mass is not connected with the hypoglossal nerve 
in series 5, but in series 518 a slender bundle unites the two structures. 
This, then, is Froriep’s ganglion. Its relation with the commissure is 
far more striking than its resemblance with a spinal ganglion. I have 
found it connected with the commissure in pigs of 17 mm., as did 
Froriep in a sheep of 12.5 mm. He considered the connection unim- 
portant and described the “vagus ganglion” as passing beneath the 
hypoglossal ganglion. In his figures (82, Pl. 16) the latter is drawn of 
the same form and texture as the spinal ganglia, and very different 
from the diffuse prolongation of the vagus ganglion. In a dissected 
pig of 17 mm. I could find no such difference: the hypoglossal ganglion 
appeared as a detached part of the ganglionic chain running for- 
ward to the vagus. This commissure in 17 mm. embryos could not 
be subdivided into definite ganglia; it was characterized by irregular 
swellings and spurs. In the adult it remains as one or two hypoglossal 
ganglia. Froriep and Beck, 95, p. 689, in all of the six hogs exam- 
ined, found a single hypoglossal ganglion and in one case two. In man 
they are quite constantly absent and the degeneration extends to the 
first cervical ganglion which may even be macroscopically lacking. 
Below the ganglion nodosum the vagus nerve gives rise to several 
branches passing between the third and fourth branchial clefts. One 
branch passes under the third cleft into the arch in front of it. There 
is a branch behind the fourth cleft and the system ends with the large 
recurrent laryngeal nerve. The laryngeal plexus appears to be derived 
from the nerves to the degenerated gill clefts. 
