CRANIAL NERVES OF SIREN LACERTINA 325 
ramus intestino recurrens situated more ventrally. It divides 
into two chief branches distributed to the floor of the pharynx lat- 
eral to the larynx. As it is recurving upon itself from the dorsal 
to the ventral position it gives off a small anastomosis to one of 
the fifth branchial pretrematic divisions. It is this ‘recurrens 
nerve’ that Wilder (1. c., p. 670) believed to innervate musculus 
interbranchialis 4. As previously noted, motor fibers may occur 
in this nerve for some distance posterior to the vagus ganglion, 
these fibers being destined for the dorsal portion of the dorso- 
laryngeus muscle. They sometimes arise from the ramus intes- 
tino-accessorius near the ganglion, sometimes independently from 
the ganglion directly. 
As to the nature of this communis recurrent nerve, peculiar to 
Siren, Driiner suggests that it represents a fifth branchial nerve, 
whose sensory part has become somewhat hypertrophied. This 
is doubtless true to some extent, for it produces a pretrematic 
ramus on the fourth branchial arch. In the opinion of the writer 
it represents as a whole the sensory component of the ramus 
intestinalis recurrens of other Urodela. This latter nerve, it 
has been noted already, is exclusively motor in Siren. This 
sensory recurrent nerve innervates the regions that in other urodel- 
ous amphibians are supplied by the sensory constituent of the 
ramus intestino-recurrens. The motor nerves to the dorsal 
portion of the dorso-laryngeus muscle, which in other Urodela 
arise from the dorsal border of the ramus intestino-accessorius, 
may arise from this sensory recurrent nerve. In Amblystoma 
the fourth branchial pretrematic (X.3,prt.) and in Amphiuma 
the fourth and fifth branchial pretrematic rami (X.3 and X.4,prt.) 
arise from the ramus intestino-accessorius. In Siren the fourth 
branchial pretrematic arises with the third from the third branch- 
ial nerve (X.2), but the fifth branchial pretrematic arises from 
this sensory recurrent ramus. Also, between this nerve and the 
fourth branchial pretrematic (X.3,prt.), anastomoses may occur. 
In its origin from the ganglion it comes from and is associated 
with the same region as the ramus intestino-accessorius. The 
writer fails to confirm Driiner’s statement that it is united with 
the third branchial nerve (X.2) in origin, but there is no improb- » 
JOURNAL OF MORPHOLOGY, VOL. 24, No. 2 
