620 'Journal of Comparative Neurology and Psychology. 



the same direction but not joining into one nerve. With further 

 growth these separate nerves would probably have merged. 



But in the sagittal sections studied, another point was brought 

 out strikingly, confirmed often by the less striking pictures seen 

 in other planes of section. If we examine a model of the brain 

 and the nerves arising from it in an embryo, where the conditions 

 are simpler than, but essentially the same as, in the adult, we 

 notice that there is a gap between the roots of the abducent nerve 

 and those of the hypoglossal nerve, where no ventral roots exist. 

 This is shown in His' models of the human brain, in the plates of 

 the brain of a I2 mm. pig embryo described by Lewis (1903. i), 

 and is figured by many others. In the human embryos studied 

 the striking feature is that this gap is frequently filled, as it were, 

 by smaller roots, emerging in the same line as the hypoglossal 

 roots, and completing a row of nerve bundles, more or less seg- 

 mentally arranged, continuing the ventral nerve roots of the cord 

 as far forward as the abducens. Moreover, in some cases these 

 roots point toward the forebrain, as though to join the abducens 

 (as in Elze's embryo) while inother casesroots situated as far for- 

 ward as these, and even fibers emerging with the abducent roots, 

 turn caudally and run as though to reach the hypoglossal nerve 

 (fig. i). (Throughout the figures aberrant roots or branches are 

 indicated by a, b, or c.) 



In two cases among the human embryos, and in a few more 

 among the embryos of pig and rabbit, the roots combine both 

 directions, so that the abducens receives a caudal root, but from 

 the loop of this a branch runs as though to join the hypoglossal 

 nerve (fig. 2). The roots which run as though to join the hypo- 

 glossal nerve, in older embryos in which the cartilage is being laid 

 down for the base of the skull, may even make foramina for them- 

 selves, in line with, but more anterior than, the anterior condyloid 

 foramen through which the hypoglossal nerve bundles run. This 

 is shown in fig. 6 from a chick embryo, in which the roots and 

 foramina are similar, but more clearly shown. McMurrich 

 (1905, p. 192) states as confirmation of the existence of four fused 

 vertebrae in the occipital bone, first described by Froriep (1886. i) 

 that "during the cartilaginous stage of the skull the anterior con- 

 dyloid foramina are divided into three portions by two cartilaginous 

 partitions which separate the three roots of the hypoglossal nerve." 

 The foramina for ventral roots of which I speak, arising near the 



