35 
of nerves behind it (“partial polymerism” of the vagus), 
then it becomes quite intelligible that vestiges of the spinal 
ganglia of these nerves should be found over the corres- 
ponding ventral roots, as is actually the case. 
Another argument for FRORIEP's and FüRBRINGER's view 
that the hypoglossus-roots have no connection whatever 
with the vagus is derived, especially by the latter, from the 
circumstance that they de not unite with the vagus but with 
the ventral roots of the anterior spinal nerves to form with 
them the cervico-brachial plexus, a fairly thick nerve stem 
which supplies, besides the anterior appendages (brachial 
plexus), the hypobranchial musculature in Elasmobranchs 
and the tongue-musculature in Amniotes where, however, the 
hypoglossus is supposed by FüRBRINGER to have eman- 
cipated from the brachial plexus. 
Branchial muscles. — In the branchial region of Selachians 
we can distinguish three groups of muscles. In the first place 
the primordial branchial muscles, known together as the 
Mm constrictores, which in VAN WYHE’s opinion (1882, p. 11) 
are to be considered as visceral muscles, taking their origin 
from the lateral plate. They are supplied by motor branches 
from the four dorsal cranial nervesw hich accordingly may be 
compared to the visceral branches of the dorsal roots of 
the trunk, connected with the sympathetic nervous system. 
Secondly we have the hypobranchial musculature (Musculi 
coraco-arcuales) from which the tongue-musculature of 
higher Vertebrates is derived. These muscles are of post-bran- 
chial origin, they are produced by ventral outgrowths or 
“buds” from the anterior trunk- and the posterior head- 
(occipital-) myotomes, similar to the myotomic buds which 
give rise to the musculature of the paired fins but 
growing out forward under the gill-slits. They are 
innervated by the branches of the plexus cervicalis — in 
Amniotes by the hypoglossus nerve—which, fused with 
the brachial plexus, runs backwards as a thick nerve stem 
from the medulla oblongata and curves round behind 
the last gill-slit to the hypobranchial muscles which it reaches 
after having separated from the brachial plexus (cf. fig. 32). 
In the third place we have the epibranchial :musculature 
(M. subspinalis and Mm. interbasales), alittle group of muscles 
attached to the pharyngobranchialia. They are found only 
in sharks and Holocephali, best developed in the primitive 
Notidanidae; in all other Vertebrates, and even in rays, 
