The fluid-filled cavity in an embryo, in the early embryonic stage, is called a blastocoele, or blastocyst cavity; this is perhaps the cavity you're referring to.
See the link below for more information on the human embryo.
coelom
How to treat internal cavities
Fistula of what? A fistual is an abnormal tubelike passage from a normal cavity or tube to a free surface or to another cavity. So depending on where the fistual is depends on the severity of the case. Fistula near rectum
No. That is false. Embryo normally get attached to uterine cavity. It is abnormal and dangerous for the embryo to get attached to fallopian tube.
A layer of cells and a cavity .
The abdominal cavity has the least protection as it has no bones to cover it.
Pisces or fish have true internal body cavity.
An internal body cavity is a space in the body that does not contain something, much like a cavity in a tooth is where the tooth has rotted away. There are several examples of this: your sinuses are internal body cavities - they are an open space in your body. There is a body cavity in your chest as well surrounding your lungs and heart.
Arthropods have an internal body cavity called a hemocoel which bathes the internal organs in nutrients, and is a component of their open circulatory system.
Probably because you can visualize the same from out side. You can list the same in internal body cavity and you wont be wrong. Mostly because the mouth and the anus both lead to the external environment.
It does actually become a body cavity, it becomes the digestive tract; the tube that passes through the body from mouth to anus.
The function of the chest cavity is to support some internal organs. The lungs and the heart are located in the chest cavity which protects and supports them.