The part nearest to the point of attachment or the attached part of something relative to the (imaginary) center of the body. For example, the start of the wing (base of the wing), the abdomen (base of the abdomen), the tibia (base of the tibia), etc.
For some structures, the use of this term can cause considerable confusion. Since the thorax will generally be considered the (imaginary) center of the body, the anterior margin (near the head) could be considered the base. Yet, in some (little used) interpretations the transition between thorax and abdomen is considered the (imaginary) center of the body, and in that case the part of the thorax that is joined with the abdomen should be considered the base. So, for the thorax it is recommended to avoid the use of this term.
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