58 



THE MUSCLES. 



iieath the eye ; and are inserted externally by means of tendinous 

 fibres into the superior border o£ the upper jaw, 



9. From the foregoing- muselé certain fibres pass to the lower 

 eyelid, which may be regarded as a depressor palpebrae inferioris 

 (Fig. 52 d.p). 



Manz^ has described a muscle as depressor palpehrae inferioris 

 which arises in the neighbourhood of the external angle of the 

 eye, somewhat behind and below the lower border of the orbit, thence 

 passes obliquely upwards to be inserted into the lower eyelid. This 

 description is right as regards the insertion, but needs correction 

 as. regards the origin. The muscle is attached to the orbital border 

 in so far that the tendinous expansion, into which the levator hulhi 

 passes at its external border, is attached into the upper jaw; this 

 bundle splits off from the upper surface of the levator hulhi at its 

 middle, and runs outwards on the under surface of the eyeball to the 

 hinder part of the lower eyelid. 



( 10. Tendon of the memhraua nlctitans'^ (^'ig"- S?> '^')" ^^^^ 

 pigmented free border of the nictitating membrane passes, at the 

 inner and outer ang-les of the eye, into a ten- 

 don which passes for some distance through 

 fibrous tissue, then descends to the under 

 surface of the eyeball and joins that of the 

 opposite side, so that the free border of the 

 eyelid, together with this tendon, form a com- 

 plete ring. The tendinous part of the ring', 

 which is thin and thread-like, is found 

 on the under surface of the eyeball, and lies 

 under the m. retractor hulfji, and is bound to 

 this muscle by connective tissue. Manz is 

 right in saying that the two muscles described 

 by Dugès as levatores palpehrae inferiores (or- 

 bito -palpebral antérieur and postérieur, n. 5 

 and 6) do not exist ; as is also the sugg'estion 

 that he has confounded the tendon of the 

 nictitating membrane with these; this is 

 clearly shown in the figure in Plate VI of Dugès. With reg-ard 

 to the actions of these eye-muscles, it is plain that the four straight 



^ Manz, Berichte der naturf. Gesellschaft zu Freiburg, 2 Band, 4 Heft, 1862, 

 p. 391- 



^ Compare Manz, L. c. 



Fig- .53- 



Eye-muscles of Rana cseu- 



lenta, from below, the m. 



recti and obliqui have 



been removed. 



n' Tendon of membrana nic- 



titans. 

 r M. retractor bulbi, lower 



part. 

 »•' Second part of same. 



