400 MABEL BISHOP 



II. Nervus opticus. In considering this and the other ocular 

 nerves, it should be mentioned that head A and head B, have a 

 normal pair of eyes and eye muscles. Nasolacrymal ducts are 

 demonstrable on each side of each head (figs. 10, 11, 13, 14, 

 16, 17, 18). 



Tracing the left optic nerve of head B from the retina to the 

 brain, it is seen to be surrounded by the origins of the muscles 



Fig. 12 Section through the motor roots of the seventh nerves of the outer 

 (normal) sides of the embryo, the hypophyses, and the upper border of the nasal 

 sacs. S. 214. 



of the eyeball and to be accompanied by the ophthalmic artery 

 on its outer and lower side. Near the eyeball it is penetrated 

 by the central artery of the retina (fig. 15) and crossed by a 

 branch of the trigeminus nerve above and by the oculomotor 

 below. It converges toward the optic nerve of the opposite 

 side (a nerve of the median region) to form a chiasma ridge 

 rostral to the developing pituitary body and spinalward of the 

 preoptic recess, which still opens into the cranial end of the 



