386 



JAMES ROLLIN SLONAKER 



branch and the cihary gangUon will be described later. The 

 other branch, the inferior, extends forward over the ventral 

 surface of the optic nerve and sends branches to the inferior 

 rectus, inferior palpebral, internal rectus, inferior oblique and 

 Harder's gland. Four of the muscles which move the eyeball 

 are thus innervated by this nerve. 



Fig. 23 Posterior view of the sparrow eye, showing the normal relative posi- 

 tion of nerves, muscles, and glands. Rex, external rectus; H, Harder's gland; 

 ohi, inferior oblique; inr, internal rectus; Rinf, inferior rectus; n, optic nerve; 

 qu, quadratus; OS, sheath of optic nerve; oh s, superior oblique; rs, superior rectus; 

 S, third nerve with its superior and inferior branches; 4, fourth nerve; 5-0, oph- 

 thalmic branch of fifth nerve; 6, sixth nerve; Py, pyramidalis; qu, quadratus; 

 Ps, posterior ciliary nerve; c, ciliary ganglion; Pi, inferior palpebral branch of 

 third nerve. 



The fourth nerve, the trochlearis, arises from the dorsolateral 

 side of the medulla. It bends around the medulla to the ventral 

 surface where it emerges at the anterior margin of the pons in 

 the groove formed by the pons and the optic lobe (fig. 18, 4-)- 

 From this point it runs almost straight forward. It passes over 

 the dorsal side of the optic nerve directly to the superior oblique 



