450 



H. V. NEAL 



Larval Scjualus. 19 



":, /n.obl.sup. m.rccT.iiii. 7 



Figs. 19, 20 Diagrams showing two later stages in the phylogenesis of the eye 

 muscles, based upon their ontogenesis in elasmobranclis The myotomes which 

 degenerate in ontogeny are indicated by dotted lines. In figure 19 the anlagen 

 of the six eye muscles are already differentiated. Their relation to the dorsal 

 and ventral moieties of the myotomes is indicated. The adult relations of the 

 muscles are seen in figure 20. They remain essentially the same in man. 

 Id, dorsal moiety of the first myotome; Iv, ventral moiety of the first myotome; 

 M, 2v, dorsal and ventral moieties of the second myotomes; 8v, ventral moiety 

 of the third myotome; a, anterior cavities; 7, seventh myotome; g.s.\ first gill- 

 slit; hyp.m, hypoglossus musculature; M, mouth; .V, nasal pit; at, otic capsule 

 sp, spiracle; Ih'r., thyreoid. 



