MURTEMJS L.^VrS. 135 



The relations of the muscle to the oculomotorius, as given 

 by Schvvalbe and confirmed by Corning, would arise if the 

 dorsal head of the muscle of my embryo should acquire an 

 origin on the sknll. The relations of the muscle to the pro- 

 fundus nerve, as given in Tiesing's figure, v^ould arise if the 

 muscle of my embryo should simply shift forward somewhat, 

 and then upward, at its origin. Its relations to the oculo- 

 motorius, as given by Tiesing, are so different from what I 

 find that his results would seem abnormal, if not in part in- 

 correct. The arrangement shown by him would arise if the 

 ventral bundle of my embryo should entirely disappeai", the 

 adult muscle being represented by the dorsal bundle only ; 

 or by supposing that the entire muscle of my embryo had 

 travelled forward at its origin beyond the oculomotorius, and 

 then backward above it. 



My embryo thus probably shows a nerve in the so-called 

 process of traversing one of the eye-muscles, and it is 

 especially to be noted that this takes place in the manner I 

 assumed in my work on Amia (3, p. 522), across the ends of 

 the muscle-fibres, and not by cutting through them mid^vay 

 of their length. The nerve, however, here traverses the 

 muscle, or more properly becomes surrounded by the muscle, 

 before the muscle has entirely acquired its origin on the 

 skull, instead of afterwards, as I assumed, the fibres of the 

 muscle growing inward, from their embryonic anlage, toward 

 the skull on both sides of the nerve, the nerve evidently 

 barring their passage, and rendering a part of the muscle 

 wholly functionless for a considerable length of time. That 

 the condition shown in my embryo is not abnormal or unusual 

 is shown by its being found on both sides of the head in both 

 my other embryos. 



The rectus externus arises by two wholly separate heads. 

 The ventro-anterior head arises from the side wall of the skull 

 immediately anterior to the trigemino-facial foramen, imme- 

 diately dorsal to the orbital opening of the canalis transversus, 

 and immediately ventral to, and in contact with, the surface 

 of origin of the ventral head of the rectus internus. The 



VOL. 45, PART 2. NKW SElllKS. L 



