Charles Russell Bardeen 243 
first formed give rise to secondary branches, the peripheral cells of the 
nerve multiply in the vicinity of the future branch and give rise to a 
tube-like projection into which the nerve-fibrils extend. In Fig. 4 at 
“a” may be seen a branch of this kind in process of formation. 
Whether a few nerve-fibrils first extend outward and then sheath-cells 
multiply so as to cover them, or the tube-like process is first formed, or 
the two processes are simultaneous, it is difficult to decide. Perhaps all 
three modes occur. 
The forward growth of the nerves takes place by essentially the same 
processes both when the growing tip represents the extremity of an 
original nerve and when it represents the extremity of a branch. In 
the cutaneous nerves, branching and forward extension is so rapid that 
the growing extremities of the nerves soon become small in calibre. In 
Fig. 9 is shown the extremity of a branch of a lateral cutaneous ramus 
of the ventral division of a 
spinal nerve of a pig 14 mm. 
long. The nerve is composed ee = — 
of a small bundle of fibrils in- eS —_ “Co 
closed by flat endothelial cells. Fria. 9. Tip of a branch of the lateral cutaneous 
BS ale ; tJq ramus of the ventral division of a spinal nerve of a 
At st a few of the fibrils pig 14mm. long. 1720 diam. 
branch off into another level. 
At “b” what appears to be a naked axis-cylinder process extends outward 
into the surrounding mesenchyme. This process is enlarged at the end 
like the two fibres pictured in Fig. 3, d. This enlargement corresponds 
to that described by Cajal as the growing extremity of a nerve-fibre. 
Unless we assume that the sheath-cell belonging to this fibre was cut 
off in sectioning, we must take the fibre to be a naked branch of the 
nerve. At ¢a few nerve-fibrils are also extending forward, but they are 
covered by a process of a sheath-cell. The more the nerves branch the 
finer the branches become. The ultimate branches consist of a few 
fibrils either naked or ensheathed by a series of greatly elongated 
sheath-cells. 
Leontowitsch has made an extensive study of the nerves in the adult 
human skin. His results, obtained by methylene-blue methods, are of 
great value, although it is probable that certain of his conclusions will 
not be accepted without further support. Leontowitsch divides the 
nerves of the skin into two groups, the medullated nerves and their 
branches, and the non-medullated nerves, or nerves of Remak. The lat- 
ter he again divides into two groups, Type I and Type II. The most 
primitive portion of the nervous apparatus of the skin, according to Leon- 
towitsch, is composed of the “‘ Remak” cells of Type I. These are cells 
