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JAMES ROLLIN SLONAKER 



the median plane of the head. These figures show also the posi- 

 tion and distribution of the nerves as' they appear in these dis- 

 sections. Figures 31 and 32, plate 6, are horizontal sections of 

 the head through the chiasma. The crossing of the fibers in 

 ribbon-like bands can be seen. 



The optic nerve enters the eye some distance toward the outer 

 and lower side from the axis of the eye. Its fibers are directed 

 downward and forward. After piercing the seclera, the main 



Fig. 20 Median section through the sparrow head, showing relations of the 

 different parts. The lower mandible and the ventral portion of the skull have 

 been removed. C, cerebrum; CB, cerebellum; H, Harder 's gland; i, inferior 

 rectus; in, inferior oblique; ir, internal rectus; M, medulla; N, nasal nerve; 

 0, optic nerve; P, hypophysis; s, superior oblique; sr, superior rectus; V, third 

 ventricle; 3, 4, and 6, third, fourth, and sixth cranial nerves. X 4. 



bulk of its fibers extend downward and forward, becoming less 

 and less numerous as they proceed, until they finally disappear 

 over the surface of the retina almost at the ora serrata. The 

 shape of the optic disc thus formed is seen in figure 22. 



The third or oculomotor nerve arises from the anterior edge 

 of the pons (fig. 18) and, running parallel with the cerebral 

 artery (6)^ bends out around the hypophysis. On reaching the 

 region of the optic nerve it divides into two main branches, the 

 superior of which runs dorsally, posterior to the optic nerve, to 

 supply the superior rectus muscle (fig. 23, S). A very small 



