152 Papers from the Department of Marine Biology. 



The obliquus superior and inferior muscles arise far cephalad from the 

 internasal cartilage and run caudal to their insertions. 



The obliquus superior arises farther cephalad than the interior muscle 

 and is inserted on the dorsal surface of the eye-ball. The obliquus 

 inferior originates a little farther back from the dorsal wall of the car- 

 tilage and lies nearer the median line. It passes mediad from the 

 superior muscle direct to the ventral side of the eye. The obliquus 

 superior is innervated by the entire trochlear or fourth nerve and the 

 obliquus inferior receives a branch of the oculomotor. 



The sixth or abducent nerve arises from a center in the medulla some 

 distance from the median line near the lateral surface of the brain. It 

 passes through a foramen in the cranial wall into the dorse-lateral angle 

 of the subcranial canal and passes direct to the lateral face of the rectus 

 externus, which it enters. 



The trochlear or fourth nerve arises from a separate center in the 

 hind-brain just caudal to that of the third nerve. It leaves the brain 

 behind the optic lobes and continues intracranially a short distance, 

 when it pierces the cranial wall, turns dorsad, and moves direct to the 

 dorsal side of the obliquus superior. 



The oculomotor or third nerve is a large nerve arising in the rnid- 

 brain from the nucleus near the median line in part mesial of the large 

 fasciculus longitudinalis dorsalis. There is no trace of the differen- 

 tiation of the large electric motor-cells at this stage. The nerve leaves 

 the brain and gives off its first branch to the obliquus inferior. Both 

 branches pass at once through the cranial wall just mesial of the rectus 

 externus. The branch to the obliquus inferior turns ventrad and passes 

 the rectus externus, interims, and inferior on its way to the ventral face 

 of the obliquus inferior. The main branch gives off another branch 

 which divides and goes to the rectus internus and inferior, but the 

 main branch itself divides again, both branches entering the rectus 

 superior muscle, a point of significance in light of further investiga- 

 tions. 



STUDY OF AN EMBRYO 14 MILLIMETERS LONG. 



The 14 mm. embryo was sectioned serially and transversely, but was 

 too poorly preserved for very careful study. The region of the electric 

 tissue on the three muscles, rectus externus, internus, and superior, is 

 now much more clearly defined and has considerably increased, but no 

 indication of electric tissue or any other muscle can be found. The 

 electric cells have enlarged slightly and can be identified by their 

 multinucleate state as well as by their dense-staining capacity. The 

 electric area is now as large as the muscle area in width, though not in 

 length (plate v, fig. 3). Nerve-fibers do not yet approach the electric 

 tissue on any of the eye-muscles. 



