ABSTRACT
Using the mamushi, Agkistrodon blomhoffii, we stained the succinate dehydrogenase activity in the infrared receptors of the pit organs by whole-body perfusion with nitro blue tetrazolium. This permitted light microscope observation of the individual receptors, or terminal nerve masses (TNMs). In whole mounts TNMs measured 20–150 μm in long diameter. The longer TNMs were possibly several receptors seen together, because serial sections showed overlapping of the edges of adjacent receptors. TNMs were also present in the scales at the dorsal and caudal edge of the pit membrane. In degeneration experiments, the perfusion technique permitted mapping of the innervation of the pit membrane by trigeminal branches: the ophthalmic branch innervated the dorsocaudal 18%, the deep branch of the maxillary the dorsorostral 46%, and the superficial branch of the maxillary the ventral 36% of the membrane. We also counted the number of myelinated fibers in these nerve trunks. Although the deep branch innervated the largest portion of the membrane, it had the fewest fibers (815, vs. 1,206 for the ophthalmic and 1,832 for the superficial). This fact, in connection with the homogeneous size of the deep branch fibers, suggested that the deep branch had the purest population of infrared fibers.
