452 Julia B. Platt 
segment, and above the region of fusion the praeoceipital arch is 
represented. Below the septum which divides the ventral part of 
the first myotome from the second, lies the fourth visceral cleft. In 
the third postotie segment is found the posterior vagus root. Along 
the path marked in fig. 25 by a shaded band, a mesodermie bud 
grows from the second myotome ventralwards, possibly joined by 
scattered cells from the first myotome, and bending around the 
posterior branchial cleft, finally extends forwards and gives rise to 
the genio-hyoideus muscle, which ultimately finds is anterior 
attachment on the mendibular arch. 
Between the second myotome and the third lies the occipital 
arch, and below this arch the fifth branchial cleft is found. Since 
the occipital arch bounds the skull posteriorly, this cleft lies in the 
region of the head. I mention this fact because SEWERTZOFF (’95, 
page 71) suggests that the intersegmental position occupied by the 
branchial clefts in Necturus may lead to »der interessanten That- 
sache, dass bei Necturus nicht alle Kiemenspalten dem Kopfe ge- 
hören«. 
From the third and fourth myotomes buds also grow ventral- 
wards in elose proximity to that from the second myotome. The an- 
terior of these buds gives rise to the muscle sterno-hyoideus. From 
the diagram it is seen that the paths described by the buds growing 
ventralwards from the fifth and sixth postotic segments diverge 
widely from one another in passing around the pronephros, but meet 
again below the pronephros in the continuous ventral longitudinal 
muscle of the trunk. 
Median to the third ‘myotome lies the first hypoglossus nerve, 
a dorsal branch from which supplies the musculature developed from 
the dorsal part of the first and second myotomes. As above men- 
tioned the ventral part of these myotomes atrophies. I have found 
no dorsal root for either of the hypoglossus nerves, although both 
nerves possess a ganglion derived in part from cells of the neural 
crest. FÜRBRINGER (’96, page 487) says that in the Amphibia the 
two first spinal nerves (the hypoglossus nerves) appear, as far as 
has been observed, to arise as complete nerves with both dorsal and 
ventral roots. With the second spinal nerve both roots remain 
throughout life. Kinaspury (’95, page 149) denies this for Necturus, 
but FÜRBRINGER considers that the denial rests on an individual 
observation since FÜRBRINGER himself found the dorsal root in the 
specimen examined. 
