IOWA ACADEMY OF SCIENCES 
265 
Tlie sheath of Henle is a rather robust structure of the primary nerve 
fibre presenting nuclei similar to those of the neurilemma. The nuclei of 
neither of these structures seem to have any regular order or position. 
These two sheaths appear to coalesce at, or slightly distal to, the point 
where the axis-cylinder breaks up into its fibrils. More evidence, how- 
ever, is desirable upon this point. The myelin or medullary sheath 
stains dark, about the same as the axis-cylinder, which would tend to 
show that this structure was nervous and not connective tissue. Inci- 
dentally this helps to settle the question — from what is the myeline 
sheath derived, whether from the axis-cylinder or from the sheath of 
Schwann? It is wanting, or nearly so, at intervals known as nodes of 
Ranvier. Divisions of the axis-cylinder occur at these nodes. These 
structures are shown in Figure 2. 
WORKS CONSULTED. 
Normal Histology. 
Methylenblautinktioh der motorischen Nervenendigungen 
in den Muskel der Amphibien und Reptilien. Archiv fiir 
Mikroskopische Anatomie. 1890. ^ 
On the Endings of the Motor Nerves in the Voluntary 
Muscle of the Frog. Studies from the Biological Labora- 
tory of Johns-Hopkins University, Vol. Ill, 1885. 
Neu Untersuchungen uber die Nerven der Muskeln mit 
besonder Borucksichtigung umstreittener Fragen. Zeit- 
schrift fiir wissenschaftliche Zoologie. LXVIII. 3. 
The nerves of the Capillaries with remarks on Nerve- 
endings in Muscle. Journal of Experimental Medicine. 
Vol. V, No. 5. 
Verbandlugen der physiologischen Gesellschaft. Jah- 
rung, 1894-5. 
Die Muskeispindeln, Kerne und Lage der motorischen 
Nervenendigungen. Archiv fur microskopische Anatomie 
und Entwicklungsgeschichte. Band. 56. 1900. 
A contribution on the Motor Nerve-endings and on the 
Nerve-endings in the Muscle-spindles. Journal of Com- 
parative Neurology, March, 1898. 
The Relation of Motor Endings on the Muscle of the 
Frog to the Neighboring Structures. Journal of Compar- 
ative Neurology and Psychology, March, 1904. 
KEY TO THE DRAWINGS. 
A and B, muscle fibres. 
a and a', nerve fibres. 
c and d, branchings other than at points where the axis-cylinder 
breaks up into .its ultimate fibrils. 
b — The point where the nerve fibre breaks up into its ultimate fibrils, 
which is usual soon after the primary fibre comes upon the muscle fibre. 
Piersol. 
Dogiel. 
Sihler. 
Sillier. 
Sihler. 
Sihler. 
Sihler. 
Huber-Dewitt. 
Wilson. 
