RECURRENT BRANCHES OF ABDUCENS NERVE 373 



and then only as two or three short nerve fibers, soon lost and 

 with no connection with the muscle. 



Dohrn'' in an early paper describes the abducens in Torpedo: 

 ''it is further noteworthy that the root fibers at their first appear- 

 ance are directed analwards, like the motor spinal nerves, and 

 that only after a certain course in this direction the separate 

 root bundles run together into a common nerve stem, directed 

 forward." This is obviously not meant to imply a recurrent 

 branch of the abducens in the strict sense; but later Dohrn* 

 did find such branches in Heptanchus cinereus. On the left 

 side of an embryo of 23 mm. he observed and drew carefully a 

 large branch running dorsalward and connecting with the myo- 

 tome called by him 'u.' He apparently did not know of Miss 

 Piatt's work, and only later of Neal's, to which he refers in a 

 foot-note. The branch was represented on the right side by a 

 much smaller nerve, reaching only half as far. He considered 

 it so little likely that such a picture should be pure chance, that 

 it became of great importance to search in the other embryos 

 to see whether in them also a ramus recurrens of the abducens 

 could be found, and in fact succeeded in finding it in a 14-mm. 

 embryo on both sides, though in a much reduced form, as a short 

 wavy nerve of only one fiber; and in an embryo of 20 mm. on 

 the left side only, also as a short branch. Thus after careful 

 search he found it in three out of some dozen Heptanchus embryos 

 studied, and in all but one case "in a much reduced form." 



Belogolowy,^ studying the cranial nerves of the chick, finds 

 frequently three groups of rootlets for the abducens, the first 

 pointing forward, the second indifferent, and the third pointing 

 mostly backward; they become, as his figures show, connected 

 with each other and with the most anterior hypoglossal roots by 

 slender bundles of fibers, making a continuous nerve parallel 

 with the floor of the medulla and prolonging the abducens cau- 

 dally to the hypoglossal nerve. This arrangement is found in 

 chicks of between three and five days' incubation, and is termi- 



3 Dohrn, 1890-2, p. 343. 



4 Dohrn, 1901, p. 28. 



^ Belogolowy, 1910, p. 271. 



