appendChain( vertex ) {

		if ( this.head === null ) {

			this.head = vertex;

		} else {

			this.tail.next = vertex;

		}

		vertex.prev = this.tail;

		// ensure that the 'tail' reference points to the last vertex of the chain

		while ( vertex.next !== null ) {

			vertex = vertex.next;

		}

		this.tail = vertex;

		return this;

	}
Appends a chain of vertices where the given vertex is the head.

@private
@param {VertexNode} vertex - The head vertex of a chain of vertices.
@return {VertexList} A reference to this vertex list.