208 EDWARD PHELPS ALLIS, JR. 
at practically the same conclusion as Swinnerton, I added the 
following foot-note to my own work (Allis, ’09, p. 195): 
Gaupp, in Bd. 3 of Hertwig’s Handbuch der vergleichenden und 
experimentellen Entwickelungslehre der Wirbeltiere, a work that I 
have only seen since this manuscript was sent to press, describes prac- 
tically similar conditions in Salmo [to those described by Swinnerton 
in Gasterosteus], and arrives at practically similar conclusions regard- 
ing the homologies of the parts. This would seem to establish the fact 
that the basioccipital portion of the myodome is extracranial in origin. 
Regarding the prootic portion of the myodome, Gaupp’s descriptions 
would seem to confirm my contention that it is an intramural space 
and not an intracranial one. 
According to the views set forth in the works above referred 
to, both Swinnerton and Gaupp maintain that the myodome 
owes its origin to the fact that certain of the muscles of the eye- 
ball, which primarily had their points of origin on the external 
surface of the chondrocranium, forced their way into the cavum 
cerebrale cranii, foreed the brain upward considerably above 
the basis cranii, and then, after having thus displaced and 
certainly disturbed the delicate central nervous organ, forced 
their way out of the chondrocranium to again acquire origin 
on its external surface, and then became secondarily enclosed 
there in a canal developed for that special purpose. This has 
always seemed to me improbable, notwithstanding my provi- 
sional and somewhat qualified acceptance of it, and I have 
long intended investigating the development of this canal when- 
ever I could obtain suitable material, my series of sections of 
somewhat advanced teleostean embryos not being considered 
suitable for the purpose. 
I, however, recently’ had occasion, in connection with other 
work, to examine a series of sections of a 5l-mm. specimen 
of Hyodon tergisus, and noticed that the myodome was di- 
rectly continuous, posteriorly, with a groove on the ventral 
surface of the basioecipital that lodged the anterior portion of 
the median dorsal aorta. This at once suggested that the basi- 
occipital portion of the telostean myodome, and hence possibly 
the entire myodome, might be a canal of vertebral origin com- 
parable to the haemal canal of the tail, for that canal is not 
