The Anatomy of Chlamydoselachus 



393 



ventral side. The combined strength of the dorsal group is obviously greater than that 

 of the ventral group. As figured and described by Hawkes the inequality in the strength 

 of these two groups is more striking. The dorsal group is strengthened to turn the eye 

 upward, not only to a moderate degree for the purpose of looking upward, but to a much 

 greater extent when the cornea is turned well under cover of the socket, for protecting 

 this most delicate part of the surface of the eyeball. The part of the eyeball (sclera) 

 then left exposed is covered with shagreen. These devices for protecting the eyes in 

 the absence of lids have been described by Gudger and Smith (1933). 



Conditions are simpler in Heptanchus as described and figured by Davidson (1918, 

 pp. 162-163 and Fig. 5). In this shark two groups of muscles (Text'figure 68) are present 

 in the orbit. The first group is placed anteriorly and consists of the superior oblique 



Rectus sup. --- 

 Rectus lat. ace. 



pectus lat. 



Fades artic. 



Rectus inf. 



Text-figure 67- Text-figure 68. 



Eye muscles of Chlamydoselachus and Heptanchus showing insertions on eyeballs. 



Text-figure 67- Semidiagrammatic figure of left bulbus oculi of Chlamydoselachus 



in medial aspect. 



The abbreviations are self-explanatory. 

 After Nishi, 1923, Fig. 2. 



Text-figure 68. Eye muscles of Heptanchus maculatus in dorsal view, right side. 



a.r., anterior rectus; i.e., inferior oblique; i.r., inferior rectus; n.II, optic nerve; o.p., optic pedicel; 



p.r., posterior rectus; s.o., superior oblique; s.r., superior rectus. 



After Davidson, 1918, Fig. 5. 



(s.o.) and the inferior oblique (i.o.). These muscles extend from the anterior part of the 

 orbit outward and caudad to be inserted on the eyeball. The second group consists of 

 the four recti muscles, all of which arise from the posterior surface of the orbit around 

 the base of the optic pedicel. The most dorsal member of this group is the superior rectus, 

 the most ventral the inferior rectus, the most posterior the external or lateral rectus, and 

 the most anterior the internal or medial rectus. They pass outward and forward to be 

 inserted on the eyeball. 



The chief peculiarity of the musculature of the eyeball of Chlamydoselachus is 

 the fact that all the muscuH recti, save only a portion of an accessory rectus lateralis 

 (externus), take origin from the eyestalk. In Chlamydoselachus the function of the eye- 



