ABSTRACT
Re-investigation of the adult human latissimus dorsi muscle (HLD) by microdissection
of acetylcho-linesterase (AChE)-stained material revealed a complicated microstructure
of this muscle. Motor end-plates distribute over the entire muscle; numerous AChE-stained
myomyonal and myotendinous junctions are interspersed. After teasing muscle fascicles
from selected representative areas, the following results were obtained.
Most of the single muscle fibers constituting the fascicles are shorter than the length
of the fascicles. They are linked together by myomyonal junctions or by myotendinous
intersections end-to-end, end-to-side, or via muscular crossbridges side-to-side,
thus forming chains and nets of varying appearance and length. Additionally, many
fiber furcations were found. These observations throw light on the microarchitectural
basis of local mass changes of the triangular HLD occurring during its convergence
from its wide lumbar and thoracic attachment line to its narrow tendon attached to
the humeral crista tuberculi minoris. The microstructural observations also explain
why motor endplates spread over the whole muscle, instead of being restricted to a
single central endplate-band, as is found in the majority of other muscles.
To clarify postnatal development, the topography of endplates in adult muscles was
compared with fetal and infantile muscles. Primarily, the endplate bands were clearly
demarcated; their width then broadened, and they gradually scattered into groups of
single endplates. Simultaneous with these developmental changes, a corresponding branching
of the thoracodorsal nerve occurs.
