ORIGIN AND STRUCTURE OF THE HEAD 101 



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 FuRBRINGER's view 

 that the hypoglossus-roots have no connection whatever 

 with the vagus is derived, especially by the latter, from the 

 circumstance that they do 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 Elasraobranchs. 

 and the tongue-musculature in Amniotes where, however, the 

 hypoglossus is supposed by FuRBRlNGER 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. 1 1) 

 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 nerves which 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-arciiales) 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 

 (Af. subspinalis and Mm. interbasales), a little group of muscles 

 attached to the pharyngobranchiaWa. They are found only 

 in sharks and Holocephali, best developed in the primitive 

 Notidanidae; in all other Vertebrates, and even in rays, 

 they have disappeared. According to DOHRN (1885, p. 



