CRANIAL SYMPATHETIC GANGLIA IN THE RAT 173 



the interval between the two stages, and is not to be thought of 

 as in the nature of a general forward extension along the internal 

 carotid of cells from the ganglion. The superior cervical sympa- 

 thetic ganglion ceases abruptly anteriorly; its cells do not 'shade 

 off' among the fibers of the internal carotid nerve. 



Especially in early stages, complementary pictures are of 

 value. The commoner methods of technique are more useful 

 in demonstrating cell elements than is the pyridine silver. While 

 the latter method has been very effective in demonstrating fibers, 

 it is of only occasional value, in early stages, in furnishing good 

 pictures of the cell bodies. The value of the pyridine-silver 

 technique improves with the increase in cytoplasm of the develop- 

 ing cell body, but even in later stages isolated cell elements 

 tend to be obscured by a wealth of heavily impregnated fibers. 

 At fourteen days little change is indicated, but in fourteen and 

 one-half day stages the pyridine-silver technique gives very 

 excellent pictures of neuroblasts — at this stage unipolar elements 

 — among the fibers of the internal carotid nerve, slightly isolated 

 from the superior cervical sympathetic ganglion. Between this 

 stage and the fifteenth day the outgrowth from the cervical 

 sympathetic ganglion extends sufficiently far forward to join the 

 great superficial petrosal nerve, and from this time on the great 

 petrosal nerve may be definitely recognized. Ganglion cells 

 found in the course of the strands vary greatly in number. 

 In one embryo (pyridine-silver technique) only a single cell was 

 observed between the superior cervical sympathetic ganglion 

 and the point of junction of great superficial petrosal and great 

 deep petrosal to form the Vidian nerve. In others cell masses 

 of considerable size have been encountered, frequently though 

 not always near the origin of the Vidian nerve (fig. 22). The 

 Vidian nerve may be followed into the sphenopalatine ganglion 

 and with it apparently go fibers from the superior cervical 

 sympathetic ganglion. In sixteen-day embryos the internal 

 carotid nerve may be traced as far forward as the carotid canal; 

 ganglion cells are encountered throughout its entire extent. At 

 seventeen days the internal carotid nerve, after giving a branch 

 to the hypophysis, fuses intimately with the abducens ; the latter, 



