SEA-FISHERIES LABORATORY. 325 



of the hyomandibular, on the internal surface of the 

 parasphenoid. They emerge from the canal into the 

 deeper parts of the orbits and are inserted into the eye- 

 balls on the inferior and middle surfaces, just underneath 

 the insertion of the inferior obliques, so that their 

 extremities are hidden by those of the latter muscles. 



The internal recti (r. int.). — Not so strongly developed 

 as either inferior or superior recti. They originate near 

 the place of origin of the superior recti on the partition in 

 the eye-muscle canal referred to. They run forwards in 

 the orbit close to the interorbital septum, and are inserted 

 into the eye-balls on the anterior and internal surface 

 underneath the extremities of the superior obliques. 



The external recti (r. ext.). — These are the most 

 slender of all the eye muscles. They take origin on the 

 internal surface of the parasphenoid far back in the eye- 

 muscle canal, and leave the latter above and externally. 

 They are inserted into the external and posterior surfaces 

 of the eye-ball. A large portion of the distal extremity of 

 each is tendinous, and contains little contractile tissue. 



With regard to the Bulbus oculi itself, we have only 

 space to mention the more striking features in its 

 anatomy. 



Blood vessels.— The afferent vessels of the bulb are 

 (1) the ophthalmic artery, the origin of which has been 

 already described, and (2) a small vessel springing from 

 the circulus cephalicus between the origins of the internal 

 carotid arteries. The efferent vessel is the superior 

 jugular vein which begins its course in the eye. These 

 vessels lie in the eye-muscle canal. They emerge from 

 the latter accompanied by the optic nerve of their side 

 with which they are bound up by a common sheath of con- 

 nective tissue. Arrived at the eye all three perforate the 



