Once you have learned to recognize and use the two major sentence patterns, you can forget about adhering to them strickly. You can combine elements of both if you wish. In that case, leave it alone. Now the sentence is both periodic and loose. Periodic structures usually expand the subject or verb.
Loose structures expand the verb or object.
Make yourself hear that pause. It is exactly the same kind of pause that occurs in your own conversation every day, in sentences like the following. That boy, the one wearing glasses , is in my history class. This piecrust, tough as it is , tastes pretty good. The class, a mixture of juniors and seniors in advanced math, read the assignment.