Dixon—On the Development of the Branches of the Fifth Cranial Nerve in Man. 31 
view that the nasal represents the first formed ophthalmic division of the fifth 
nerve, for it will be seen that, in Rv., the sum of the length of the frontal, together 
with that of the common stem of the ophthalmic, does not equal the length of the 
nerve already present in Br;., whereas it is evident that the nasal in Ru. can 
represent the nerve present in Br;. The appearance of the posterior and 
shorter frontal branch, in Ru., is that of a nerve in a very early stage of its 
growth, ze. it stains darker than it will later on, and more nuclei are present 
Br3(4 weeks). 
2Osa) 
qe Ru.(sth week). 
ea) 
= 
12.6 -~.. 20— esa 
— ~-~--Lfrontal, CR Geginning of 
ine 26 Ail S “"" 6th week) 
FM(7 weeks). 
Mr.(8th week). 
Fieure 1, 
Diagram to illustrate the relative lengths of the different branches of the Ophthalmic Nerve in five different human embryos 
The actual length of the nerves is in each case x 26 times and given in mm. No attempt has been made to represent the 
courses taken by the different nerves. 
among its fibres. That the nasal is the first branch of the ophthalmic to make its 
appearance in the human embryo, corresponds with what may be observed in the 
rat. In this animal, also, the frontal nerve is formed later than the nasal, but its 
growth is more rapid. Ina rat embryo of the 14th day the ratio of the length 
of the frontal to that of the nasal nerve is 4%, while on the 15th day the 
ratio is 3y. 
