182 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
2. Splitting of an Elongated Protoplasmic Body (cord or tubule), We 
may recognize here two sub-processes : (a) splitting at the tip, and 
(4) splitting along the whole length. 
a. Asis well known, nerves grow out as blunt stalks which repeatedly 
divide at their ends. Paterson has shown that some of the spinal nerves 
split at the somato-splanchnic angle, as shown in Figure 11. His (788, 
Fia. 11. 
Arch. f. Anat., Jahrg. 1887, p. 376) shows in many cases that the split- 
ting takes place where the end of the growing nerve strikes a rigid organ. 
Thus, he says, when the third branch of the trigeminus strikes Meckel’s 
cartilage, it divides into the ramus lingualis and the ramus mandibularis ; 
amd when the hypoglossal meets the jugular vein, it divides into its de- 
scending and lingual branches. The way in which the rigid organs act 
to produce splitting is thus explained by His, Pre-existing resistant ob- 
jects may be considered as the “Motivs” of division; for as a nerve 
Fig. 11. Cross section of a mouse embryo in the lumbar region, showing the 
splitting of the spinal nerve at the upper angle of the colom. After Paterson, ’91, 
Trans. Roy. Soc. London, CLXXXL, Fig. 5. 
