Innumerable such asanas have been described in detail in Sthananga, Brihatkalpabhashya, Uttaradhayana, Moolaradhana, Yogashastra etc. Whatever posture we sit in, it becomes an asana. It is believed that the asanas are of 84 lakh types. They got reduced to 84 asanas when they were made compact. The study of those asanas was probably done on the basis of the observation of animals and birds. There is an asana called mayurasana. How does a peacock sit? After studying the way the peacock sits, it was felt that the peacock has a tremendous digesting capacity. It can digest whatever it eats. Therefore, mayurasana was prescribed to keep ones digestive system in good order. When one does the mayurasana, he adopts a ball mudra. Then there is an asana called matsyasana. It is natural for fish to remain on the surface of the water. It never gets drowned. It is believed that those who are learning how to swim would not get drowned if they move on in the matsyasana posture. It is also the asana that helps one to resist. The matsyasana should be definitely done after doing the sarvangasana.