MORPHOLOGY OF TRANIAL ^FUSCLES IX SOME VERTEBRATES, 243 



11,^ III/ and Y ~ ; in the fourth branchial seo-ment only a 

 coraco-branchialis IV is formed. This condition — of an 

 interarcualis venti-alis I and coraco-branchiales II, III, IV, 

 and V — persists till stage 63 ; at a later stao^e the hinder end 

 of the iiiterarcualis veiitralis I grows backwards, forming, 

 in the specimen examined, a longitudinal muscle, which is 

 attached posteriorly to the fifth bar, and also a coraco-bran- 

 chialis I. From this and the descriptions given of the adult 

 by M. Fiii-bringer and by Jaqaet, it may be inferred that 

 the hind end of the interarcualis venti-alis I always grows 

 back, forming a coraco-branchialis I, and may or may not 

 also grow back to a more posterior branchial bar. 



The portions of the branchial myotomes immediately above 

 the interarcualis ventralis I and coraco-branchiales II, III, 

 and IV form Mm. margjnales." No adductors are developed. 

 The upper ends of the first four branchial myotonies and the 

 whole of the fifth branchial myotome above the coraco-bran- 

 chialis y (no fifth M. marginalis being developed) form 

 levatores arcuum branchialium^ (Text-fig. 48). 



The trapezius'' is proliferated from the outer side of the fifth 

 levator in stage 48 (Text-fig. 48). 



In Xecturus (]\Iiss Piatt), in embryos of 12^ mm. there is 

 an outgrow' th from the ventral part of the glosso-pharyngeal 

 muscle — the beginning of the cerato-hyoideus internus; and 

 there are three constrictors arcuum, the first growing forwards 

 from the mesotlielium of the first vagus arch where this joins 



' M. chiasiiiiqiie of Ja(|uet : second and tliird Mm. iiiterbrancliiales 

 o£ Greil. 



- The posterior margin of the traiisversus ventralis Y in stage 63 

 iniderlies the lung. 



^ M. brancliialis of Jaquet ; first, second, third, and fourth Mm. 

 interbranchiales of K. Fiirbringer : f oui-th and fifth Mm. interljrancbiales 

 of Greil. In the adult, according to Jaquet. these muscles are attached 

 dorsally to the upper ends of the branchial bars, according to K. 

 Fiirbringer to the skull. 



* Cranio-branchiales of Jaquet ; levatores arcuum liranchialium of 

 Greil. 



* M. scapulo-brancliialis of Jaquet ; levator scapulte of Greil. 



