EYE OF THE ENGLISH SPARROW 387 



which it innervates (fig. 23, 4)- In its course it lies close to the 

 orbital wall, outside of the external and superior rectus muscles, 

 until near its termination, when it dips under the superior 

 oblique and branches over its bulbar surface. 



The sixth nerve, the abducens, arises from the ventral sur- 

 face of the medulla near the median line (fig. 18, 6). It runs 

 forward almost parallel with the trochlear nerve to the posterior 

 side of the optic nerve. Here it divides into two parts (fig. 23, 

 6). The larger division turns sharply outward and passes 

 under the external rectus where it divides into fine branches 

 which penetrate the bulbar side of this muscle. The smaller 

 division passes under the rectus muscles close to the eyeball. Its 

 course is upward over the dorsal side of the optic nerve and down 

 the anterior side where it finally terminates in the pyramidalis 

 muscle. It thus almost encircles the optic nerve. In the region 

 of the quadratus it gives ofT branches which innervate this muscle. 



The fifth or trigeminus nerve arises at the side of the anterior 

 portion of the medulla by two roots (fig. 18, 5). These unite at 

 the Gasserian ganglion {g) a short distance from the medulla. 

 At the distal margin of the Gasserian ganglion the ophthalmic 

 nerve (o) is given off. This runs forward and enters the orbit 

 posterior to the optic nerve. Its course is in a dorsal and an- 

 terior direction around the eye (fig. 23, 5). It leaves the orbit 

 at the anterior margin near the region of the duct from Harder's 

 gland. In its com'se through the orbit it runs almost parallel 

 with the trochlearis. Just aftfr entering the orbit it lies be- 

 tween the external rectus and the orbital wall. It then passes 

 under the superior rectus, just dorsal to the optic nerve, over the 

 quadratus and under the superior oblique to its exit from the 

 orbit. In the region of the optic nerve a small branch is given 

 off, which runs under the muscles to the eyeball where it turns 

 downw^ard and joins a branch from the ciliary ganglion (fig. 24, 

 bo, figs. 21 and 22, b). 



The long and short ciliary nerves in the sparrow are derived 

 from the oculomotor and the ophthalmic nerves, as already 

 stated. A more detailed description will, however, be neces- 

 sary, as some variations have been found. 



