PROCEEDINGS OF SOCIETIES. 309 
of making thin sections, and thereby deranging the relation 
of all the finest and most delicate structures. Such a muscle 
I have found in the extensive mylo-hyoid of the little green 
tree-frog (Hyla arborea.) The elementary fibres of this 
muscle are scarcely more than the ,,),,th of an inch = -0036’” 
in diameter; and as there are but two layers, the fibres of 
which are at right angles to each other, all the structures in 
the muscle can be demonstrated most beautifully. The very 
long thin muscular fibres are not too close for exact obser- 
vation. The vessels can be readily injected.* 
These specimens have been prepared upon the same plan 
as others, and are preserved in glycerine, which enables me 
to press the thin muscle and separate the fibres further from 
each other, while the finest fibres of the nerves are prevented, 
by the viscid medium, from breaking or from being so com- 
pressed amongst the other tissues as to be destroyed or ren- 
dered invisible. The muscle must be prepared when quite 
fresh, otherwise the fine nucleated fibres are completely dis- 
integrated. The capillaries were injected as in the other 
cases. tT 
In this thin muscle, networks formed by bundles of dark- 
bordered fibres, consisting of from two to five or six, may be 
very easily shown, and with high powers (700 to 3000 dia- 
meters) the very fine nucleated fibres resulting from the 
division and subdivision of these in a dichotomous { manner, 
can be readily demonstrated. 
In this thin muscle I have often followed individual fine 
nucleated nerve-fibres, now over, now under muscular fibres, 
sometimes crossing transversely, sometimes obliquely, and 
sometimes running for a certain distance parallel to the fine 
muscular fibre. The drawing accompanying this paper ren- 
ders further description unnecessary. I shall enter into full 
detail in my communication next session; but as the summer 
* The very thin and wide intercostal muscles of the Chameleon, after 
having been soaked in glycerine, may be separated into two layers, external 
and internal intercostals, in each of which the finest ramificatious of the 
nerve-fibres may be followed, and their relation to the sarcolemma demon- 
strated. The long elementary fibres of the thin tubular part of the tongue 
of the same animal are also favorable for this investigation ; but the Chame- 
leon is only to be obtained ‘occasionally, and the muscle of the green tree- 
frog, above referred to, possesses many advantages. 
+ As the details of the mode of preparing these specimens would occupy 
many pages, I must defer entering into this part of the question; and it is 
useless to give the outline, as success depends entirely on minutiz. 
+ The dichotomous division is most common; but sometimes three, four, 
or even five branches result from the division of one fibre, as is well known 
to be the case in the common frog. 
