HYOMANDIBULA OF THE GNATHOSTOME FISHES 565 
sensory nerves, but it lies dorsal to the latero-sensory fibers 
that issue with and as a part of the nervus hyomandibularis 
facialis. 
In the Teleostomi, Hochstetter does not give either the method 
of development or the composition of the definitive vena jugu- 
laris. I find this vein, on one side of the head of a 43 mm. em- 
bryo of Amia calva, running posteriorly ventral to the ganglion 
on the main root of the nervus trigeminus and then upward 
between that ganglion and the ganglion on the root of the nervus 
facialis; then posteriorly dorsal to the latter ganglion, and dorsal 
also to the latero-sensory fibers which issue with the nervus 
hyomandibularis facialis, but ventral to the latero-sensory fibers 
which issue with the nervus trigeminus; then downward between 
the nervi facialis and glossopharyngeus; and then posteriorly 
ventral to the latter nerve and the vagus: the first section of the 
vena capitis lateralis that is formed in this fish thus correspond- 
ing to the one said by Hochstetter to be first formed in reptiles. 
On the other side of the head of this embryo of Amia the vena 
jugularis had a similar course, but a large branch of it passed dor- 
sal to the nervus glossopharyngeus and then downward between 
that nerve and the vagus to fall again into the main vein, this thus 
showing a second section of the vena capitis lateralis in process 
of formation. In one adult specimen of Amia I find the vein 
running ventral to the nervus trigeminus, dorsal to the nervi 
facialis and glossopharyngeus but ventral or lateral, and hence 
morphologically ventral, to the latero-sensory nerves which issue 
with the nervi trigeminus and glossopharyngeus, and then ven- 
tral to the nervus vagus. The definitive vena jugularis of Amia 
is thus formed by the trigeminus and vagus sections of the vena 
cardinalis anterior and the facialis and glossopharyngeus sec- 
tions of the vena capitis lateralis, and it corresponds, not only to 
the second stage in the formation of the definitive vein in reptiles, 
as given by Hochstetter, but also to the definitive vein (vena 
petroso-lateralis) of amphibians as given by Driiner (’04). The 
conditions in the one embryo examined would seem to show that 
no other sections of the vena capitis lateralis are ever formed 
in Amia. 
