Researches on the development of the muscular fibres of the heart, and
on voluntary motion. By Dr. Lebert.—Towards the thirty-sixth
hour of incubation, the contractions of the heart of the embryo chick
are distinct and regular: nevertheless, at this time the structure of the
heart presents only organo-plastic globules surrounded by granular
matter. The primal structure of the embryo heart is the same in all
vertebrate animals ; and in many lower animals, such as the compound
ascidia (e. g. Jlmorucium, Milne Edwards), it constitutes the permanent
condition. An undoubted difference between these and the globules of
the heart’s structure may be established from their earliest appearance.
This obtains equally with the globules of the hearts of the embryos
of mammalia and of fishes : the batrachians alone seem to form an ex-
ception, and in these there is rather resemblance than identity between
the two kinds of globules.
From the third to the fourth day of incubation the structure of the
heart assumes a more diffused appearance. The cellular envelopes of
the organo-plastic globules in great part disappear. At this time a su-
perficial layer of fusiform elements may be distinguished, which after-
wards becomes the pericardium.
From the fourth to the fifth day there may be noticed for the first
time in the midst of the globular elements, elongated cylindrical bodies
arranged in reticulated groups. These, the inorganic cells or bodies,
constitute the first rudiments of the muscular fibres, and whether in
the heart, or in the voluntary muscles, whether in the superior verte-
brata or in the batrachians, these always precede the development of
the true muscular fibre,which, indeed, constitutes but a higher degree
of their development. M. Lebert has not been able to observe the for-
mation of these cells or bodies by regular lineal allocation of plastic
globules. Some included globules which are noticed, must be considered
accidental: they are wanting in those of the embryo mammiferi, which,-
however, they surround externally. The absence of nuclei and nucle-
oli in these bodies does not disprove their cellular character, since the
same feature is found in the globules of the vitellus of the chick, and
of the dorsal cord of the embryo frog. The myogenic bodies, though
generally roundish, are at first irregular in form in the superior ver-
tebra ta.
After the seventh or eighth day, the plastic globules notably diminish,
and entirely disappear some days later. The muscular fibres gradu-
ally assume their longitudinally striated aspect. Their inlernal granules
arrange themselves in groups in the direction of the length of these
bodies, which correspond to the primitive, fibres of authors. The trans-
verse markings of the fibres are not seen until much later, and it is
not until toward the expiration of embryonic life that they are constantly
seen. The fibres of the voluntary muscles are formed later than those
of the heart, from five to six days after the heart has fully commenced
its functions. To give an idea of the distance of time that separates
the development of the heart from that of the muscles of voluntary mo-
tion in mammifers, it may be stated that the former is seen in the em-
bryo of the bat when .078 of an inch in length, whereas the latter is
only met with in embryos of about half an inch in length (0.468.)
A reverse order obtains in the tadpole, in which a necessity exists
for early movement in the fluid in which it floats, in order to seek its
nourishment. In proportion to this necessity is the early develop-
ment of the voluntary muscles in all embryos.—London Med. Gazette
from Comptes Rendes.