The roads or highways, by land or sea, designated by law as the avenues over which the mails shall be transported. Railway Mail Service Cases, 13 Ct CI. 204. A “post route,” on the other hand, is the appointed course or prescribed line of transportation of the mail. U. S. v. Koch ersperger, 26 Fed. Cas. 803; Blackham v. Gresham (C. C.) 16 Fed. 611.