MUSCLES OF CERATODUS 345 



are inserted into the ventral ends of all five Cerato-branchialia. 

 The fasciculus inserted into the first is confluent with the 

 anterior part of Subarcualis rectus v. 



Innervation. — According to Fiirbringer and Greil, Sub- 

 arcualis rectus i. is innervated by the IXth. I can confirm 

 this. According to Fiirbringer the Cleido-branchialis is 

 innervated by the Plexus cervicalis ; according to Greil 

 both the Subarcualis rectus v. and the Cleido-branchialis are 

 innervated by the N. ultimus vagi (Quartus Vagi), i. e. the nerve 

 to the fifth branchial arch. I can confirm Greil's statement. 



The Subarcualis rectus i. s. Branchio-hyoideus is homologous 

 with the similar muscle in Lepidosiren, Protopterus, and 

 Amphibians. Its innervation is not known in these Dipnoans. 

 In Amphibia, as in Ceratodus, it is innervated by the IXth. 



The morphological nature of the hinder longitudinal muscles 

 is uncertain. Fiirbringer held that the Cleido-branchialis 

 is homologous with the Coraco-branchiales of Selachii. Greil 

 did not express any opinion other than that quoted above. 



The muscles in Ceratodus are developed from a single 

 primordium which grows forward from the fifth branchial 

 arch. The posterior end of the muscle gains a secondary 

 relation to the Cleithrum, and subsequently an almost complete 

 separation into two muscles takes place. The shoulder-girdle 

 is situated far forwards and has an oblique position — from 

 dorso-posterior to ventro-anterior — its lower part underlying 

 the branchial region. If this represents the phylogenetic 

 development of the muscles, as is probable, the original form 

 was probably a Subarcualis rectus v., passing from the fifth 

 to the first Ceratobranchial, and the Cleido-branchialis is 

 a secondary muscle. The developmental evidence thus leads 

 to rejection of Fiirbringer 's theory. 



It is not known whether there is a Subarcualis rectus v. in 

 Protopterus and Lepidosiren, but Fiirbringer described a 

 homologue of the Cleido-branchialis in these Dipnoans and 

 stated that the innervation is, as in Ceratodus, from the Plexus 

 cervicalis. 



The Subarcualis rectus v. is probably derived from a Sub- 



