OBLIQUE SMOOTH-MUSCLE BUNDLES BETWEEN THE CIRCULAR AND LONGITUDINAL MUSCLE LAYERS IN THE CANINE PROXIMAL COLON

The region between the longitudinal and circular muscle layers of the canine proximal colon was investigated by light and electron microscop y. Unique smooth muscle bundles, referred to as ''oblique'' muscles, w ere arranged in branching/anastomosing bundles, forming a network inte rmeshed with the nerve plexus and vasculature. These smooth muscles we re concentrated along the ganglia and primary connectives of the myent eric plexus, thus showing a periodic distribution roughly correspondin g to that of the ganglia. The oblique smooth muscle bundles bridged th e distance between the circular and longitudinal muscle layers and ble nded into the inner aspect of the longitudinal muscle layer and the ou ter aspect of the circular muscle layer. A few oblique muscle cells oc curred within the sheath of the ganglia and primary strands, i.e., per ineurium. Oblique muscles may serve to electrically couple the circula r and longitudinal muscle layers, thus explaining the synchronous elec trical activities of these muscles. It is possible that the pacemaker activity in the myenteric region is generated by these muscle cells. O blique muscles may also serve to protect nerve elements and the vascul ature from the mechanical stress of peristalsis.