Identify the location and function of the following: $HIV$ Antigen and Amniotic bag.

(N/A) $(1)$ $HIV$ Antigen:
- Location: Found in the blood of a patient suffering from $AIDS$.
- Function: Detection of $HIV$ antibodies or antigens is used for the diagnosis of $AIDS$.
$(2)$ Amniotic bag (Amniotic sac):
- Location: Surrounds the developing embryo in the uterus.
- Function: It contains amniotic fluid,which protects the fetus from mechanical shock and allows for amniocentesis (a prenatal diagnostic test) to detect genetic disorders.