RECURRENT BRANCHES OF ABDUCENS NERVE 387 



nerves and runs medially and ventrally to join the tympanic 

 branch from the petrosal ganglion of the glossopharyngeal nerve, 

 median to the gasserian ganglion, to form with it the small 

 superficial petrosal nerve. It is to be considered, therefore, 

 merely as the motor facial component to this nerve, which arises 

 more cranially than usual and takes a separate course, at a 

 considerable distance from the geniculate ganglion. It passes 

 through a separate foramen in the precartilage of the base of 

 the scull. 



On the right side of this embryo there is again no forward- 

 running abducens nerve; the external rectus muscle is supplied 

 by a branch of the oculomotor. But in the usual position of the 

 abducens roots fibers arise which turn ventrally, slightly caudally, 

 and laterally to join the motor division of the facial nerve, distal 

 to the geniculate ganglion. Thus a ventral root from a position 

 slightly cranial unites with a lateral root just beyond the ganglion 

 of the accompanying dorsal fibers, and the relations of a complete 

 nerve are closely approximated. 



Applying to this case the ideas gathered from the study of the 

 recurrent branches of the abducens, I examined the eye muscles 

 of this embryo, and also the various parts of the eye itself. The 

 external rectus muscle was clearly differentiated on both sides, 

 the eyes were apparently normal, though the retina and lens 

 w^ere in a poor state of preservation. But in comparison with 

 other embryos of the same size and even smaller, it was found 

 that the eye and all its appurtenances were definitely retarded. 

 The retina was thinner and less differentiated, the lens showed 

 shorter fibers and was still widely vesicular, the eyelids ^vere 

 less developed and the anterior chamber was not even suggested, 

 though already present in other embryos of 18 mm. As a whole, 

 the eye of this embryo resembled most closely that of a 14.5 

 mm. embryo. With this retardation of the eyeball, the eye 

 muscles were found to be much smaller than usual, though 

 clearly differentiated. 



The probable history of the abducens nerves in this embryo 

 can, then, be sketched as follows: all of the emerging fibers were 

 submitted to the caudal attraction of the postotic musculature 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 28, NO. 2 



