MUSTELUS L;RVIS. 133 



gemino-facial ganglion, and separated from it by nienibraue 

 only. Running forward and laterally in this position to the 

 anterior edge of the foramen, it there turns upward, mesial to 

 the truncus buccalis-maxillo-mandibulavis, and immediately 

 enters the rectus exteruns. 



Tiesing shows the abducens in the adult issuing by a 

 separate and independent foramen, the foramen lying dorsal 

 to the trigemino-facial foramen, which seems a singular 

 position for it. 



Eye-Muscles. 



The rectus superior arose in my large embryo mainly 

 from the dorsal edge of the trigemino-facial foramen, but 

 apparently also in parb from the tough membrane that closes 

 the foramen around the nerves that issue through it. A part 

 of the muscle here lies between the dorsal edge of the fora- 

 men and the dorsal surface of the issuing nerves. Its surface 

 of origin thus lies posterior to the profundus foramen, and the 

 latter nerve lies, as it issues from its foramen, anterior, or 

 even slightly antero-dorsal, to the muscle; but it is evident 

 that this relation of muscle and nerve is not morphologically 

 different from that said by Tiesing to exist in the adult, the 

 nerve there lying antero-ventral to the muscle. The muscle 

 of the embryo would simply have to travel at its origin 

 slightly dorsally to produce the conditions found by Tiesing 

 in the adult. 



The rectus inferior arises from the side wall of the skull 

 immediately posterior to the profundus foramen, and partly 

 surrounding the hind edge of that foramen. The surface of 

 origin of the muscle lies dorso-posterior to that of the rectus 

 internus, and as the muscle runs outward, downward, and 

 forward, it passes between the two heads or bundles of the 

 latter muscle. 



The rectus internus is represented by two bundles of 

 fibres, the ventral and larger one of which arises from the 

 side wall of the skull between the profundus and trigemino- 

 facial foramina, lying ventral to the one and anterior to th^ 



