Provide definitions/explanations for the following terms:
$(1)$ Heterodont
$(2)$ Appendix

(N/A) $(1)$ Heterodont: In humans and many mammals,teeth are of different types based on their shape and function. These are categorized into four types: Incisors,Canines,Premolars,and Molars. This condition of having different types of teeth is known as heterodont dentition.
$(2)$ Appendix: The caecum is a small blind sac which hosts some symbiotic micro-organisms and is located at the junction of the small and large intestine. $A$ narrow,finger-like tubular projection,known as the vermiform appendix,arises from the caecum.