Inhalation is aided by use of external intercostals, scalenes, and sternocleidomastoid muscles. These nerves include the intercostals, phrenic, and abdominals. During inhalation the external intercostals contract, as does the diaphragm. Works the lungs, tones up the intercostals and diaphragm. Smaller muscles between the ribs, the external intercostals, assist with this process. The intercostals pull the ribs backwards or forwards. The intercostals are a set of muscles sandwiched among the ribs. The lumbar arteries are in parallel with the intercostals.