Innervation of the dermatomes in the neck of the mouse.

The dorsal rami of the cervical and thoracic spinal nerves were investigated using both the in situ cholinesterase staining technique and cholinesterase staining on serial sections of plastic-embedded embryos. In most cases only the dorsal rami of the 2nd to 5th cervical spinal nerve possess cutaneous branches. The area innervated by the cutaneous branch of the dorsal ramus of the 5th spinal nerve borders on an area innervated by the cutaneous branch of the dorsal ramus of the 1st thoracic spinal nerve. The dorsal rami of the cervical spinal nerves 6-8 show no cutaneous branches. Therefore the gap in the series of the dorsal cutaneous branches is due only to the middle part of the nerves of the brachial plexus, which range from the 5th cervical nerve to the 1st thoracic nerve.