U.S. Patent Act
..Part II. Patentabililty of Inventions and Grant of Patents
....Chapt. 11. Application for Patent
The applicant shall furnish a drawing where necessary for the understanding of the subject matter sought to be patented. When the nature of such subject matter admits of illustration by a drawing and the applicant has not furnished such a drawing, the Commissioner may require its submission within a time period of not less than two months from the sending of a notice thereof. Drawings submitted after the filing date of the application may not be used
(i) to overcome any insufficiency of the specification due to lack of an enabling disclosure or otherwise inadequate disclosure therein, or
(ii) to supplement the original disclosure thereof for the purpose of interpretation of the scope of any claim.