200 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



ance during succeeding stages have been described. In the present stage, 

 it lies caudad and mediad of the eyeball. The main mass of the muscle 

 extends laterad until its outer extremity comes to lie just veutrad of the 

 ophthalmic branch of the trigeminus (Plate 7, Fig. 25, mu. rt. p.). From 

 this main portion an arm extends mediad and caudad to meet the abdu- 

 cent nerve ; the nerve penetrates the muscle mass, and its fibrils become 

 thoroughly intermingled with the cells of the fundament. 



The fundaments of the dorsal, ventral, and anterior rectus and the 

 dorsal oblique muscles were all seen for the first time in Stage III. The 

 dorsal rectus (Plate 7, Fig. 26, mu. rt. d.) extends in a transverse direc- 

 tion, its outer end lying dorsad of the ophthalmic branch of the trigemi- 

 nus, and its inner end dorsad of, and in close contact with, the oculomotor, 

 immediately before that nerve reaches the ciliary ganglion. 



The common fundament of the ventral and anterior rectus muscles 

 (mu. rt. v. + O") is comparatively large, and lies along the ventral side 

 of the optic stalk, reaching laterad as far as the third nerve, which lies 

 along its ventral border. 



The most superficial of all the muscle fundaments is that of the dorsal 

 oblique, which lies in the same parasagittal plane as the Gasserian gan- 

 glion, and is dorsal to the eyeball at a point a little anterior to one 

 opposite the choroidal fissure. This is the only eye-muscle fundament 

 which does not appear in the plane of the section of which Figure 26 is 

 a photograph. It has no connection with its nerve, the trochlear, which, 

 indeed, I have not been able to detect up to this stage of development. 

 In appearing thus before its nerve, it resembles the posterior rectus 

 muscle, and differs from the muscles innervated by the oculomotor. 



The last muscle to develop is the ventral oblique (Fig. 26, mu. ob. v.), 

 which first appeared in Stage IV. Its fundament is antero-ventral to 

 the optic stalk, and much nearer the median plane than the dorsal ob- 

 lique. The axis of the muscle fundament extends transversely, and near 

 its median end receives the spreading fibrils of the extremity of the 

 oculomotor nerve. It is the only one of the muscles finally innervated 

 by the third nerve into which fibrils from the nerve can at the present 

 time be traced. 



Notes on Later Development. 



1. Oculomotor Nerve. In Stage V (about five days' incubation) none 

 of the branches of the third nerve found in the adult were present. In 

 series of about seven days' incubation it can be seen that the eye-muscle 

 fundameuts, which in Stage V were in contact with the sides of the 



