This is a picture of a traditional big band. The front row is saxes, the second trombones, and the third trumpets. On the side is the rhythm section.http://www.yankeehomecoming.com/Day4.html
Tommy Dorsey had his own big band as seen on the previous brass quintet or larger ensembles like symphony orchestras . Sometimes Tommy Dorsey combined different types of groups to make a new sound, for example sometimes he included more string instruments in his band.
A traditional jazz band includes
5 saxophones
4 trombones
5 trumpets
1 piano
1 guitar
1 bass
1 drum set