CRANIAL NERVES OF SIREN LACERTINA 327 
that he interprets it as a posttrematic ramus of a fifth branchial 
nerve. There is also found a possible representative of a sixth 
posttrematic ramus. In Siredon, as in other Urodela, the truncus 
intestino-accessorius X is plainly a nerve of multiple origin. Ex- 
cluding the accessorius, lateral line, and posterior intestinal con- 
stituents, there is left a ramus intestinalis recurrens of motor and 
communis composition which represents parts of one or more 
posterior branchial nerves, that in certaia respects have become 
much hypertrophied. If we consider the laryngeal cartilages 
as representatives of posterior branchial arches of urodelan an- 
cestors, then the muscles connected with these cartilages and 
innervated by the ramus intestino-recurrens: musculi dorso- 
laryngeus, laryngeus ventralis, and so-forth, must be regarded as 
modified branchial muscles. There is beginning, or has already 
taken place, a considerable usurpation by the ramus intestino- 
recurrens, of territory of the ventral branchial region belonging 
orginally to the posttrematic rami of the primitive branchial 
nerves. The musculi subarcuales, and interbranchialis 4, and to 
some extent the ceratohyoideus internus muscle, innervated by 
the ramus ‘intestino-recurrens, are muscles which originally had 
no relation to that nerve, but have been appropriated to some 
extent by it. In consequence of this usurpation the ramus recur- 
rens has been disproportionately enlarged as a branchial nerve, 
and the third to fifth or sixth branchial nerves have undergone 
a variable amount of atrophy. Driiner believes that, in the com- 
mon progenitors of the Selachians and the Urodele Amphibians, 
there must have been present at least seven branchial arches 
between the hyoid arch and the shoulder girdle. 
In Siren the fourth branchial nerve is represented by a ramus 
pretrematicus, (X.3,prt.), which takes its origin from the pharyn- 
geal division (X.2,ph.) of the third branchial nerve, rather than 
from the ramus intestino-accessorius X as in most Urodela. With 
this r. pretrematieus there may anastomose a pharyngeal branch 
(fig. 48, s-r.1) of the ramus recurrens sensitivus X. The repre- 
sentative of a ramus posttrematicus is seen in the nerve which 
innervates the levator muscle of the fourth branchial arch (lab.4). 
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