Abstract
The main object of this study has been a comparative
survey of the distribution of motor neuromuscular junctions
in vertebrate skeletal muscle, and the principal method
employed has been the histocheraical demonstration of these
as sites of cholinesterase concentration.
In so vast a field as the skeletal musculature of
vertebrates, some discrimination has been necessary in the
selection of material for study. The observations are
therefore presented in three sections.
In the first section, a study is made of the distribution
of motor endplates in the segmental musculature of a
representative series of lower vertebrates, from Amphioxus
to reptiles. Observations of cholinesterase distribution
have been supplemented by silver staining and electron
microscopy to give a fuller picture of the morphology and
innervation of segmental muscle.
The second section deals with avian muscle. As will be
discussed, the muscles of birds appear to be built up of two
varieties of muscle fibre which differ in their mode of
innervation. The attempt has been made, therefore, to
demonstrate these two forms of innervation by histochemical
means.
The patterns of endplate distribution in a series of
mammalian muscles are described in the third section,
together with certain additional observations made to try to
determine the significance of some forms of endplate
distribution.
In the discussion which follows, the histochemical
demonstration of cholinesterase in skeletal muscle is first
considered, and then the results of the three sections are,
in turn, compared with those of previous workers, and their
significance assessed. The effectiveness of the combination
of techniques used in the present work is evaluated, and
the occurrence of cholinesterase at muscle- tendon junctions
is examined. From the literature, instances are quoted
of the main reasons that have been put forward in favour of
the subdivision of skeletal muscle fibres into two distinct
types, and it is considered how far the results of the
present studies may fit in with these hypotheses.
Utilising certain information gained in the course of
this work, a series of experiments was carried out to try
to determine the site, or sites, on a skeletal muscle fibre
at which growth in length takes place. These experiments
are described, and the results considered, in the final
section of the Thesis.
