626 "Journal of Comparative Neurology and Psychology. 



we see representatives of the two groups mentioned above; for 

 there are fibers with a lateral course which pass behind the vagus- 

 accessory trunk, and others which pass, or at least point, in front 

 of the vagus, behind the glossopharyngeal nerve. In another 

 embryo (fig. i) a laterally running ventral root not only passes in 

 front of the vagus, but actually joins with a separated bundle of 

 the glossopharyngeal nerve, making a complete ventral root for 

 this nerve. 



If we examine the embryos of birds and reptiles, even those of 

 large size, we find conditions which throw light on these aberrant 

 nerves in man and other mammals. In the turtle and the chick 

 there are almost constantly found segmentally arranged roots 

 from the ventral part of the medulla almost as far forward as the 

 abducens, smaller than the main roots of the hypoglossal, of which 

 there are two, with two foramina, on each side (Bronn's Thier- 

 reich?), but still often joining the main roots to form the trunk, 

 and always making foramina for themselves (fig. 6). The most 

 anterior of these small roots often arises opposite the glosso- 

 pharyngeal nerve, and runs as though to join it, and not the hypo- 

 glossal nerve, outside the skull. Moreover, from each of the 

 roots of the hypoglossal nerve, except often the most anterior 

 rudimentary ones, a large branch runs laterally and dorsally, as 

 soon as the root leaves the foramen. Here then we are dealing 

 with branches similar to the dorsal rami of spinal nerves, or at 

 least the motor portion of such rami. These fibers in the spinal 

 nerves innervate the muscles of the back, the dorsal rami of 

 the upper cervical nerves going to the trapezius, which in mammals 

 is innervated chiefly by the accessory nerve; but in birds and 

 reptiles the hypoglossal nerve has dorsal rami running to the 

 muscles that correspond to the trapezius, and, as we might expect 

 in birds and reptiles the accessory nerve is either lacking, or runs 

 as part of the vagus; its place is taken by the dorsal rami of the 

 hypoglossal nerve. 



I consider these aberrant fibers which run laterally in the 

 embryos of man and other mammals as vestiges of the dorsal rami 

 of the hypoglossal found in birds and reptiles, whose place is taken 

 in mammals by the accessory nerve; or, if arising nearer the abdu- 

 cens and running in front of the vagus, as vestiges of the dorsal 

 ramus of a ventral root of the glossopharyngeal nerve. 



- Bd. 6, Abth. iii, i, p. 149, and Bd. 6, Abth. iv, i, p. 3S9. 



