MORPHOLOGY OF CEAXIAL MUSCf-ES IX SOME VEKTEBTIATES. 309 



advanced above, are somatic in origin, (b) Nerve-fibres of a 

 less maximum diameter (12*8 n, in some dogs only 11'2 fx), 

 are found in the nerves of the mylohyoid, facial and platysma 

 muscles, palatal, pharyngeal, and laryngeal muscles and crico- 

 thyroid — all C)f which, according to the theory advanced 

 above, are splanchnic in origin ; and also in the nerves of 

 the lingual muscles, which are developed from the genio- 

 hyoid — a somatic muscle. 



Herrick stated that the nerve-fibres of the branchial 

 muscles of Menidia were characterised by their large size, 

 and supposed — on the theory that these muscles were of 

 splanchnic origin — that they had acquired this somatic 

 feature. On the theory advanced above, however, the bran- 

 chial muscles are somatic in origin. 



The small size of the nerve-fibres of the lingual muscles is 

 curious, but the muscles, though somatic in origin, have 

 intimate relations to a splanchnic epithelium. This sugges- 

 tion is supported by the measurements of the nerve-fibres 

 passing to the genio-hyoid and lingual muscles of Lacerta 

 viridis and Testudo mauritania; in the former animal 

 the maximum diameters found are 11 "6 and 9'G/< respectively, 

 Avhereas in the latter animal both maxima are the same, viz. 

 7*5 //. 



I have, in conclusion, to express many thanks to Prof. 

 Salensky for embryos of Acipenser ; to Prof. Bashford Dean 

 for embryos and for the loan of sections of Ceratodus; to Prof. 

 Graham Kerr for specimens of P o 1 y p t e r u s s e n e g a 1 u s ; and 

 to Prof. Fawcett for the loan of sections of the pig; also to 

 the last-named for much kindness shown to me during many 

 years in his laboratory. 



Literature. 



Aicar ('()8). — "The Development of the Skull and Visceral Arches in 

 Lej)idosiren and Protopterns." " Trans. Roy. Soc. Edin..* vol. xlv. 



('')8j. — ■■ The Deveiopinent of the Anterior Mesoderm and Paired 



Fins with their Xerves in Lepidosiren and Protoptenis," • Trans. 

 Roy. Soc. Edin.," vol. xlv. 



