382 JOHN LEWIS BREMER 



true, the growth of the abducens rootlets spreading backward 

 toward the hypoglossal nerve. This generalization is, I think, 

 too broad, and was probably made after the study of only the 

 two classes of embryo mentioned in his paper, namely, the chick 

 and the pig. It also might properly be amended to include 

 the other ventral cranial nerve, the oculomotor, arising still 

 farther forward. With this in view, I have examined embryos 

 of sheep, pig, and rabbit, and find in each that, as Belogolowy 

 states, the abducens roots emerge serially from before backward, 

 and that in each the development of the oculomotor nerve pre- 

 cedes that of the abducens. In man, on the other hand, if one 

 may judge by the four embryos available at this critical stage, 

 the abducens is the earlier of the two nerves, and the growth 

 wave spreads forward. The oculomotor nerve seems to grow 

 much faster and reaches the eye muscles sooner than the abdu- 

 cens, which would lead to a false idea of their relative priority. 

 Thus the first rootlets of the abducens are probably the caudal 

 ones, nearer and therefore more suceptible to any postotic attrac- 

 tion; while in the other mammals studied the earliest rootlets 

 are cranial and therefore removed from this attraction and 

 brought nearer to a pre-otic influence. Both influences act 

 apparently even as far back as the first human roots, vying with 

 each other and causing the divergence of the individual fibers. 

 The attractions suggested are, of course, the masses of develop- 

 ing muscle, the pre-otic eye muscles rapidly developing, and the 

 postotic premuscle mass either degenerating or migrating for- 

 ward, according to the two prevalent theories of the loss of the 

 postotic myotome. In the human embryo of 6 mm. mentioned 

 above, in which the abducens fibers are short and turn, some 

 cranially, some caudally, and in which the oculomotor nerve is 

 as yet absent, the occipital muscles are already indicated by a 

 continuous band of elongated cells in the somites extending as 

 far forward as the vagus ganglion. Ventrolateral to this ganglion 

 and again ventrolateral to the glossopharyngeal, facial and 

 trigeminal gangha, there are condensations of mesenchyma, but 

 without elongated cells. After a gap there is again a mesenchy- 

 mal condensation dorsal and caudal to the eye, in which elon- 



