Prevalence of touch sensation (sparshanendriya-vyapaktva)

There are much more topics in our Ayurvedic classics about which we have limited knowledge. Like this an another topic is Indriya. We don't know what is indriya or what are their sites. Are the organs by which we perceive sensation called Indriya or different from them? Acharya Charaka has told five types of Indriyas, Sparshanendriya, Chakshurendriya, Ghranendriya, Rasanendriya & Shravanendriya. He also described their sites, functions, composition, and their properties. But he also told that Sparshanendriya is the main Indriya and it is present in all Indriyas. Why Charaka told that Sparshanendriya is Vyapak in all Indriyas. Is this concept wrong or right? The answer is right & this concept can be proved by following means as described in this paper.