Explanation

Digestive system in mammals comprises an alimentary canal and concerned digestive glands. Human gut or alimentary canal consists of mouth $\rightarrow$ buccal cavity $\rightarrow$ pharynx $\rightarrow$ oesophagus (food pipes) $\rightarrow$ stomach $\rightarrow$ small intestine (duodenum $\rightarrow$ jejunum and $\rightarrow$ lleum) $\rightarrow$ large intestine (caecum $\rightarrow$ colon $\rightarrow$ rectum). The large part of large intestine terminate into 2-3 cm long anal canal and its opening is called anus. So, the correct chronological order is descending part of colon $\rightarrow$ rectum $\rightarrow$ anus