In Ayurveda, the body is not described as head, stomach, legs, etc. It is described as:
1. Three guna and dosha — each of which have five parts
2. Five types of prana
3. Seven layers of substances called dhatu which begin with semen and end with skin.
4. Five gross material elements
Ayurveda did not believe in the existence of the body as modern science describes — lungs, heart, spleen, stomach, intestines. Surgery was a relatively late addition to Ayurveda.
It is not that they cannot see these body parts. But they don’t consider it real. They just consider it your sense perception. What lies behind that sense perception? That’s what Ayurveda is.
What you call ‘head’ and ‘brain’ doesn’t exist in Ayurveda. There are five senses, some of which are in the region of the head, but like skin, they are also spread all over the body.
The best description of mapping between the visible body and the Ayurveda system of the body is that they divide the body by the three guna. The part of the body from the head to the heart is dominated by the guna-dosha of kapha. So, if you go to an Ayurvedic physician and say you have a brain tumor, they will not perform surgery. They will cure the dosha of kapha. Similarly, if you say you have migraines, they will try to cure the dosha of kapha. If you have a lung infection or throat infection, they will still try to cure kapha. This is how they think of the body.
Likewise, any disease in the middle of the body — from the heart to the genitals — they consider disease of pitta. And anything in the hands and legs — e.g. joint pain — they consider the disease of vata. This is the high-level classification of the body in terms of three dosha.
But you must remember that this type of classification is always a fractal structure. So, within this high-level division, there are smaller divisions as well. For example, the eyes in the head have a top-level classification of kapha but a lower-level classification of pitta. Similarly, the nose is a higher-level classification of kapha and the lower-level classification of vata. And they also try to understand whether these three dosha have expanded from subtle to gross or from gross to subtle. If this expansion has occurred then the cure takes a longer duration.
In this way, there is a theory of the body, and they cure based on this theory. They don’t look at body parts in the way modern medicine does. The only exception is the division of surgery — which I said is relatively recent — and which looks at body parts like modern surgery.