596 
we describe the peripheral connexion of nerves 
with the various tissues and organs, and it is 
much to be regretted that our knowledge in 
reference to that connexion is scarcely more 
complete or accurate than that of their origin. 
The only instance in which we can speak 
pretty confidently respecting the tk eons 
connection of nerves, is with regard to mus- 
cles. In the striped muscle, nerves appear to 
form loops, the convexities of which are di- 
rected across the fibres of the muscles. Each 
nerve-fibre passes at first parallel to the direc- 
tion of the muscular fibres, and then crosses 
them in an arched form to pass back into the 
bundle from which it had emerged, or to be 
mingled with the fibres of some neighbouring 
bundle, passing back in it to the centre, pro- 
bably to some part of it different from the 
place of origin of the nerve. As far as present 
means of observation enable us to judge, there 
does not appear to be any other connexion be- 
tween the nerve-tubes and the muscular fibres 
beyond the simple contact of the tubular mem- 
brane of the former with the sarcolemma of the 
latter. We have no evidence of any mingling 
of the true nerve-substance with the sarcous 
elements, and, therefore, we are forced to con- 
clude that whatever be the nature of the in- 
fluence which nerve exerts upon muscle to pro- 
voke it to contraction, that influence is exer- 
cised through the two layers of homogeneous 
membrane which form the investments of the 
nervous and sarcous elements respectively. 
The best mode of observing the disposition 
of nerve in muscle is to examine under the 
microscope very thin and transparent muscles 
of some small animals. The abdominal mus- 
cles of the frog first afforded to Hales, and long 
after him to Prevost and Dumas, this opportu- 
nity; the muscles of the eyeball in small birds 
were used by Valentin; Burdach examined the 
muscles of the frog’s tongue; I have found the 
intercostal muscles of the mouse very suitable 
for the purpose. 
Peripheral expansion of nerves on sentient 
surfaces—With regard to the disposition of 
nerves on sentient surfaces (the skin, for ex- 
ample) the most probable view appears to be 
that they are disposed in a plexiform manner, 
The nervous trunks pass toward the surface 
dividing and subdividing, the ramifications pass- 
ing backwards to the centre in conjunction with 
neighbouring bundles; so that, whilst a very 
intricate plexus is formed, the looped arrange- 
ment, similar to that described in muscle, pre- 
vails, the convexities of the loops being di- 
rected towards the deep surface of the integu- 
ments. Gerber states, that in those parts of 
the skin which are provided with papille, the 
nerve-loops pass into the bases of the papille 
and form an element of their composition; and 
he adds, that in some instances the nerve-tube 
which forms the loop exhibits tortuosities or 
convolutions similar to those which are seen 
upon bloodvessels. According to the same 
author, in parts of the skin where the tactile 
sensibility is acute, the meshes of the nervous 
lexus are extremely small, whilst they are of 
bite size where the skin is not highly sensitive. 
NERVOUS SYSTEM. (Nerve.) 
The arrangement of the primitive fibres in — 
loops has been seen by Henle on some parts 
of mucous membrane, in the membrana nie 
tans of the frog for example, and in the 
cous membrane of the throat in the same ani- 
ition has been described 
mal. A similar dis 1 
and delineated by Valentin on the pulps of the — 
teeth. ( Fig. 333.) ™~ 
Fig. 333. 
sharin | on at se of the a a 
of t jaw in t. » showing ‘an 
apo (From Valoctin ) L 
Retina and optic nerve-—The examinat 
of the peripheral connexions of the net 
of pure sense has not thrown light om # 
general question. The peripheral expat 
of the optic nerve or the retina prese 
the elements of a nervous centre; th 
matter is present in it in considerable 
tity, and certain fibres continuous with the 
mitive nerve-tubes are likewise expanded 
But the connexion of these fibres with 
matter has not been detected here any more 
in the centres themselves, nor has any arr 
ment of looping or of plexuses been di 
strated. Mr. Bowman has been led, by: 
examinations, to the opinion that these 
are the central parts of the nerve-fibre (the 
of Remak) which have been deprived ¢ 
tubular membrane and of the white sut 
of Schwann. It is worthy of notice that 
called optic nerve itself presents certain p 
characters, which entitle it more to be r 
as a prolongation of the nervous 
than as a distinct nerve. The nerve-tubes’ 
are met with in it are for the most part 
minute size; they admit of separation 
great difficulty, owing to their not being 
posed in fascicles like those of other ¢ 
spinal nerves: they appear to be surrou 
by and deposited in an abundant gi 
blastema, in which there seems to be } 
scattered elements of grey matter. . 
