Is professor responsible if his postgraduate medical student's dissertation is not approved ?

In medical education, post graduate (PG) student's dissertion work needs to be approved before he/she can write the final examination.The idea of making the dissertation compulsory was to evoke interest in research work among the PG students.The dissertation work is usually the first step of research for a student and he needs help and guidance from his teacher. The professor or associate professor is given the responsibility of acting as guide for their PG students and signs in the dissertation document that the work was done under his supervision and guidance throughout the study period.I had corrected many dissertations and rejected few of them for basic deficiencies in  data  entry,irrelevant contents just to fill the pages,too many grammatical mistakes,duplication,falsification of data etc.I wonder how his guide signed those documents overlooking all these?.

The risk of rejection…