Hi 



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SKCT. 



go, to their insertion round the equator of the eye. One of them 

 is dorsal in position, and is called the superior rectus (s. r.), a 

 second ventral, the inferior rectus {in. r.), a third anterior, the 

 anterior or internal rectus (i. r.), and a fourth posterior, the 2JOsterior 

 or external rectus (e. r.) The usual names (internal and external) 

 of the two last-named muscles originate from their position in 

 Man, where, owing to the eye looking forwards instead of out- 

 wards, its anterior surface becomes internal, its posterior surface 



Fid. 787, B.— Section of the iiiiiua! cye-of Sphenodon. /», lilmnl-vcssel ; h, cavity of eye, filled 

 with fluid; L-, connective-tissue capside ; I. Icus : .1/. lunlecular layer of retina; /•, layer of 

 rods and cones ; st, nerve ; .f, cells in nerve. (I'roni Wiodersheini's t'crteOrata, after Baldwin 

 Spencer.) 



external. The two remaining muscles usually arise from the 

 anterior (in Man inner) corner of the orbit, and are inserted 

 respectively into the dorsal and ventral surface of the eye-ball. 

 They are the s)iperior {s. o.) and inferior oUiquc (i. a.) muscles. 



The median or jjineal eye (Fig. 787, B), is formed, in certain cases, 

 from the distal end of the epiphysial di\crticulum already men- 

 tioned. It has tlie ibi'm of a rounded capsule, the outer or 

 anterior j^tji'tion of the wall of which is a lens (I.) formed of 

 elongated cells, while its posterior jiortion has the character of 



