162 CHARLES EUGENE JOHNSON 



proaches the eye-ball, along the surface of which it extends 

 towards its insertion which it reaches quite simultaneously with 

 the M. obliquus superior, in embryos of about 11 mm. It then 

 graduall}^ straightens out, and grows directly towards its origin. 

 The first branch developed from the oculomotor nerve goes to 

 this muscle and is given off where the nerve crosses its dorsal 

 posterior border to reach the ciliary ganglion. 



The Mm. rectus inferior and rectus medialis are the last of 

 the eye muscles to begin their development, and they arise from 

 a common anlage which is formed by a deep out-pocketing from 

 the ventro-lateral wall of the first somite, just mediad of the 

 M. obliquus inferior. This is the condition at the 10-mm. stage. 

 A thickening of the walls of this out-pocketing, especially on the 

 posterior and ventral sides, takes place simultaneously and it 

 becomes transformed into a solid elongate mass. By the 11-mm. 

 stage a constriction has appeared, slightly beyond the middle of 

 this mass, differentiating it into a proximal M. rectus inferior 

 and a distal M. rectus mediaUs. The distal end of the M. rectus 

 inferior now lies where its insertion later occurs. The distal 

 end of the M. rectus medialis swings gradually dorsal ward in 

 the direction of its future point of insertion on the eye-ball, in 

 front of the optic stalk. Its proximal end, which at first is con- 

 tinuous with the distal end of the M. rectus inferior, works up 

 along the medial side of this muscle so that the final separation 

 of the two takes place at their proximal ends, i.e., their ends of 

 origin. This has just occurred in the specimen with an 8.5-mm. 

 carapace. Their insertions have by this time been established, 

 and the muscles are directed toward their points of origin. In 

 the 11-mm. stage each of these muscles has received its branch 

 from the N. oculomotorius. 



In regard to the origin of the abducent and oculomotor nerves 

 Filatoff makes the following italicized statements: 



Meiner Ansicht nach ist es von grosser Bedeutung, den ersten Zustand 

 des Auftretens der Anlage, welche zwar keinerlei Nervenclemente ent- 

 hiilt, doch in Form und Lage den kiinftigen Nerv praformiert, d.h, 

 also den Umstand in Auge zu behalten, dass diese Anlage in innigstem 

 und ununterbrochenen Zusammenhange mit der Anlage des Muskels 



