178 



relaxation of the wall of the reeessiis and the contraction' 

 of the eye muscles effect the retraction of the eye-ball. If 

 the eye in a fresh or living: fisl^ l*^ §'6iitly pressed fluid 

 passes into the recessus from the orhit and the former can 

 be seen to swell. 



The eye muscles (text-fig. 5) are the usual six pairs, 

 two pairs of oblique muscles, and four pairs of straight 

 muscles or recti. 



The superior oblique muscles {Ohl. Sujj.). — Both right 

 and left muscles lake origin on Ihe left side of the head. 

 It will be remembered that the left prefrontal sends back- 

 wards a long process which fits into a groove on the dorsal 

 surface of the parasphenoid. At the beginning of this 

 process the prefrontal is deeply grooved for the reception 

 of the ethmoid cartilage, the groove being formed by two 

 horizontal bony lamina?, and on the upper of these laminae 

 and on the adjacent anterior concave surface of the pre- 

 frontal the oblique muscles take origin. The left superior 

 muscle passes upwards and slightly backwards along the 

 left side of the interorbital septum to its insertion on the 

 eye-ball. The right muscle, however, immediately passes 

 through the ethmoidal fenestra and so through the inter- 

 orbital septum to the right orbit. It then passes upwards 

 and backwards, diverging slightly from the left muscle, 

 along the right side of the interorbital septum to its inser- 

 tion in the right eye-ball. 



The insertion of these miiscles is peculiar. Each 

 splits up near its distal extremity into anterior and 

 posterior slips. The anterior slips (ohl. suj>.), which are 

 the larger of the two, have wide insertions on the superior 

 and anterior surfaces of the eye-balls. The posterior slips 

 (o. s. .t'.) curve round the internal and superior surfaces of 

 the eye-balls, crossing over the insertions of the superior 



