Morphology and Development of Endomysial Connective Tissue in Porcine and Bovine Muscle

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Abstract
Endomysial reticular fibers were demonstrated in frozen muscle sections using an ammoniacal silver nitrate method. From birth to 198 kg live weight in pigs, the thickness of endomysial sheaths in the longissimus muscle increased from approximately 1 µm to 4 micrometers. In neonatal muscle, endomysial sheaths were composed of fine, randomly oriented argyrophilic reticular fibers but those in adult muscles were dominated by thicker argyrophilic reticular fibers mostly oriented perpendicular to longitudinal myofiber axes. Stretching of a pre-rigor muscle sample as it was frozen caused a re-orientation of reticular fibers so that lattices of endomysial sheaths were widened longitudinally and many reticular fibers became oriented at an acute angle to longitudinal myofiber axes. Strong argryophilia (black staining) was absent in individual reticular fibers wider than approximately 2 to 4 µm and was lost in smaller reticular fibers which were steam-heated. In bovine muscle, endomysial sheaths from tough muscles of the distal forelimb were not appreciably thicker than those of the lumbar longissimus muscle. Endomysial sheaths were polygonal in cross section with pentagons and hexagons being the most common shape. Angles of histological transection of endomysial sheaths were calculated from the relationships between minimum and maximum widths of cross sections. In the porcine longissimus muscle at the level of the first lumbar vertebra, approximately half a million endomysial sheaths were transected at an angle of 40° to their longitudinal axes. Copyright © 1975. American Society of Animal Science . Copyright 1975 by American Society of Animal Science.

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