Vomeronasal organ. The vomeronasal organ (VNO), or the Jacobson's organ, is an auxiliary olfactory sense organ that is found in many animals. It lies close to the vomer and nasal bones. It was discovered by Frederik Ruysch prior to 1732 and later by Ludwig Jacobson in 1813. This organ is the sense organ involved in the flehmen response in mammals.
In the 19th century, the postal system continued to grow. The Post Office Department, which had been founded to oversee the Postal Service, developed new services and established new post routes. As the United States grew dramatically between 1789 and 1861, when the Civil War broke out, its population also increased.
The United States issued its first postage stamps in 1847. Before that time, the rates, dates and origin of the letter were written by hand or sometimes in combination with a handstamp device. Since enactment of the Postal Reorganization Act of 1970, postage rates have been set by the Postal Regulatory Commission.