per·i·neu·ri·um 
(pĕr′ə-nrē-əm, -nyr-)
(pĕr′ə-nrē-əm, -nyr-)n. pl. per·i·neu·ri·a (-nrē-ə, -nyr-)
The sheath of connective tissue enclosing a bundle of nerve fibers.
[New Latin : PERI- + Greek neuron, nerve; see NEURON.]
per′i·neuri·al adj.