Muscle Structure

Intercalated discs join the membrane of one cardiac cell with its neighbour and promote rapid conduction of depolarisation between cells.

[Ref. Junqueira 15th] 

Smooth muscle fibers are individual small, fusiform (tapering) cells, linked by numerous gap junctions.Thin and thick filaments in smooth muscle fibers do not form sarcomeres, and no striations are present. Branching is absent.

Aortic opening of diaphragm at the level of T12

Except rich blood supply all are the criteria of white fibers

Myofibrils are the structural and functional subunits of muscle fiber. Myofibrils are arranged longitudinally in the muscle fiber and runs in the entire length of muscle fiber.

Sarcomere is the structural & functional unit of myofibrils. 

The substance of the tongue is made up chiefly of skeletal muscle supported by connective tissue. The muscle is arranged in bundles that run in vertical, transverse and longitudinal directions. This arrangement of muscle permits intricate movements of the tongue associated with the chewing and swallowing of food, and those necessary for speech.

Visceral striated muscles:
These are microscopically identical to the skeletal muscles, but they are confined to the viscera such as tongue, pharynx, peripheral part of the  diaphragm, and upper two third of esophagus.