The trunk is a fusion of the upper lip and the nose, and it contains no skeletal element and no joint. Movement comes instead from the arrangement of muscle around a fixed volume of tissue, a structure biologists call a muscular hydrostat, shared with squid arms and vertebrate tongues. Because the tissue cannot be compressed, contracting muscle in one direction forces elongation, bending or stiffening in another.
Estimates of the number of individual muscle units run into the tens of thousands, and the often-quoted figure of about forty thousand is a modelled count of small fascicles rather than a direct dissection tally. The tip differs between the two African species and the Asian elephant: African elephants have two opposing finger-like processes, Asian elephants one.
A persistent error is that elephants drink through the trunk as through a straw. They draw water part-way up the nasal passages, then curl the trunk and squirt it into the mouth. Nor does an elephant breathe through its mouth in ordinary circumstances; the trunk carries almost all respiration.