The presence of transverse and axial tubules in the ventricular myocardium of embryonic and neonatal guinea pigs.

Developing transverse (T) tubules are found in embryonic guinea pig ventricular myocardium after approximately eight weeks of gestation. By the time of birth (nine weeks total gestation); longitudinally-oriented axial tubules connected to the T tubules also have formed, and the majority of cells closely resemble those of the adult. The form taken by the developing T and axial tubules suggests that they are generated in a manner similar to that for T tubules in chick and rat skeletal muscle, namely by repeated formation of caveolae.