392 



Bashford Dean Memorial Volume 



from mesodennal segments (head somites) which are serially homologous with those of 

 the trunk (Text-figure 62). In primitive fishes, the head somites, Hke the trunk somites 

 of vertebrates generally, are at first hollow and their cavities communicate with the 

 primitive coelomic cavity. In other words, the coelomic cavity extends into the somites. 

 In the head, this communication is by way of the mesoderm of the branchial arches, 

 as shoum (for Torpedo) in Text-figure 65 after Corning. Van Wijhe (1883, Figs. 1 and 2, 

 Taf. I) gives more exact drawings showing the same features in Scyllium canicula. These 

 channels quickly close, and the somites later become solid structures. 



i^- ■ pi.t.ain:- praf. V 



, -* Ob'.iquus inf. 



> 1 '"■ 



R. maxiUomp.ndib. V. 



Text-figure 66. 

 Dorsal view of the eye muscles of Chlamydoselachus on the right side. 



The Roman numerals distinguish the nerves supplying the eye: 11, second cranial or optic nerve; III, third 

 cranial or oculomotor nen.'e; IV, fourth cranial or trochlear ner%-e. Other abbreviations are self-explanatory. 



After Nishi, 1923, Fig. 1. 



In Chlamydoselachus, the muscles of the eyeball and their innervation were described 

 from two specimens by Hawkes U906), and later by Nishi (1922) who used four adult 

 specimens. They were considered briefly by AlHs (1923), who merely supplemented the 

 work of Hawkes by comparisons with his own specimens. 



The disposition of the various eye muscles of Chlamydoselachus is shown in Figures 

 10, 11, and 12, Plate IV; also in Text-figures 66 and 67- It will be seen from Text-figure 67 

 that the dorsal side of the eyeball has three muscles, while only two muscles supply the 



