MUSCLES OF CERATODUS 851 



Goppert (1904), subsequently, in Protopterus. Tliese writers 

 employed the term ' Constrictor pharyngis ' on the theory that 

 it represents the musculature of atrophied hinder branchial 

 segments. But the theory receives no support from the 

 developmental phenomena in Lepidosiren, as described by 

 Agar (1907), nor could I see any evidence in its favour in 

 Ceratodus. I have therefore employed the term ' Sphincter 

 oesophagi et laryngis '. 



Agar stated that the ventral portion of the Sphincter 

 oesophagi et laryngis of Lepidosiren is derived from cells budded 

 off from the inner walls of the pericardio-peritoneal ducts, and 

 its dorsal portions from downgrowths of the occipital myotome y 

 (' possiblj^ but not probably, the downgrowth extends to x 

 and z also '). These two constituents coalesce and form a 

 complete sphincter muscle. 



As, however, the ventral part of the Sphincter is continuous 

 anteriorly with Transversus ventralis v. in all three adult 

 Dipnoi, and this is not excluded by the figures given by Agar 

 of the first stage of its development in Lepidosiren, it is possible 

 that this part is, as in Ceradotus, due to a backward extension 

 of Transversus ventralis v. 



The ventral part of the sphincter of Lepidosiren is said by 

 Agar to be innervated by the N. muscularis vagi. This is 

 apparently the nerve of the fifth branchial arch, and the 

 innervation w^ould thus agree with that of Ceratodus. But 

 the description given by Pinkus of the innervation of the 

 muscles in the branchial region in Protopterus is very vague, 

 and exact information is needed. The dorsal portion of the 

 Sphincter of Lepidosiren is innervated, in accordance with its 

 derivation, by Nervus occip. y (Agar) ; Lepidosiren and 

 Ceratodus are similar in this respect. 



Larynx. — Neumeyer (1904) stated that the larynx is 

 developed in a 10-9 mm. embryo immediately behind the 

 branchial region, Kellicott (1905) that it developed in a 11-6 mm. 

 embryo in the ventral wall of the pharynx near the commence- 

 ment of the oesophagus, Greil (1913) that it developed in a 

 11-6 mm. embryo at the level of the fifth branchial segment, 



