39 
the 4th (5tt) — 8 post-otic somites. As we shall see 
below, they are partly intra- and partly post-cranial. 
Finally, in Amniotes the relation of the occipital myotomes 
to the gill-slits has not been determined with equal exact- 
ness as in Anamnia by those who adhere to the view that 
both correspond. But, taking as an example VAN BEMMELEN'’s 
(1889, p. 254) instructive figure for Lacerta, we see that 
here too five myotomes contribute to the formation of the 
hypoglossus musculature, beginning with the first more or 
lest rudimentary myotome to be observed in the occipital 
region. The most probable conception seems to me to be 
that this belongs to the third post-otic somite (the second 
being that of the primary vagus). If this be right, this 
somite is at the same time the last epibranchial one, since 
the number of gill-pouches, being five, corresponds to that of 
Amphibians. The hindmost of the five myotomes mentioned 
above is post-cranial and corresponds to the atlas. According 
to CORNING (1895, p. 165), it is only from the 2nd — 5th 
of these myotomes that the hypoglossus-musculature in 
Lacerta is derived, the first becoming rudimentary. In this case 
no epibranchial myotome would participate in its formation. 
hus on the whole we may say that the hypoglossus 
musculature originates from post-branchial myotomes and 
that, if epibranchial myotomes contribute to its formation, 
their number is yet not greater than one. NEAL (1897, 
p. 461) suggests that a temporary forward crowding of the 
visceral clefts which causes the last epibranchial somite to 
lie above and not in front of the last gill-cleft, as observed 
by himself in Acanthias and by Miss PLATT (1898, p. 458) 
in Necturus, may permit the ventral growth of this myotome 
which would otherwise be prevented. Among the above 
investigations, however, the only statement relating to the 
participation of the last epibranchial myotome that has not 
been opposed is that of Miss PLATT for NECTURUS, and here 
the fact that the innervation is performed only by the first two 
free spinal nerves seems not wholly to exclude doubt. 
he number of the myotomes producing the hypoglossus 
musculature may vary and we get the impression that on 
the whole it is greater in forms where also the number of 
gill-slits under which this musculature will come to lie is 
greater (Petromyzon), less in forms with less gill-slits (Am- 
phibians, Amniotes). However, this is not a rule without 
exceptions, since e.g. in rays, to judge from the number 
