ZOOLOGY 



SECT. 



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 posterior 

 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 



at 



FIG. 787, B. Section of the pineal eye of Sphenodon. g, blood-vessel ; h, cavity of eye, filled 

 with fluid ; k, connective-tissue capsule ; 1. lens ; M . molecular layer of retina ; r, layer of 

 rods and cones ; st, nerve ; x, cells in nerve. (From Wiedersheim's \ r ertebrata, 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 superior (s. 0.) and inferior oblique (i. 0.) muscles. 



The median QT pineal eye (Fig. 787, B), is formed, in certain cases, 

 from the distal end of the epiphysial diverticulum already men- 

 tioned. It has the form of a rounded capsule, the outer or 

 anterior portion of the wall of which is a lens (I.) formed of 

 elongated cells, while its posterior portion has the character of 



