HISTORY OF THE EYE MUSCLES 



435 



mobranchs (VanWijhe '82, Miss Piatt, '91, Lamb '02), Rep- 

 tiles (Corning '00, Filatoff '07, Johnson '13), Mammals (Miss 

 Fraser '15). 



One point, however, in the ontogenesis of the eye-muscles from 

 the head-cavities still remains in dispute. While most investi- 



ng. 1 A camera drawing of a parasagittal section of a 7 mm. Squalus embryo 

 (Series IFF-2-2-16) showing the head cavities. The anterior cavity, not seen by 

 Marshall but later discoverd by VanWijhe, is also shown. It soon degenerates 

 while the other cavities differentiate into the eye muscles. A, anterior head 

 cavity; 1,2,3, first, second and third head cavities; VII. ac, acustico-facialis nerve 

 anlage; cl.crs.n, neural crest cells; gn.V, trigeminal ganglion; ot, otic capsule; 

 sp, spiracular pouch; tb.n, neural tube. 



gators agree with Marshall in deriving the external rectus muscle 

 from the third (hyoid) cavity, Dohrn ('04) and the writer 

 ('09) have asserted that the second (mandibular) cavity also 

 participates in its formation. Neither, however, published any 

 figures or other evidence to support his assertion. The first, 

 question, therefore, to which we may well turn our attention 



