South of the Kane fracture zone (23 o 40'N), the Mid-Atlantic ridge is segmented into 20-100-km-long spreading cells in which morphology, seismic and gravity signatures change along and across the ridge-axis. The rift valley, considered as a typical structure along slow-spreading ridges, can be symmetric or asymmetric, and segment centers experience strong magmatic activity whereas low magma supply results in thinning of the crust at segment tips. Along the segment centered on the Snake Pit neovolcanic ridge (23 o 22'N), the rift valley is clearly asymmetric, and mantle and lower crustal rocks are commonly exposed on the steepest and highest ridge flanking wall. In this area, we analyzed submersible observations (Gravinaute cruise) collected up to 50 km on both sides of the axis to discuss the proceses responsible for the axial valley shape, its possible relationship with ''deep'' rock exposures, and to determine the origin of off-axis structures. Our data reveal that the structure and the geology vary on both walls of the axial valley and is different from the volcanic and tectonic organization observed on the neovolcanic ridge itself. Furthermore, the structure of the off-axis domain in different from the axial valley and rift mountains are organized in a set of regularly spaced relief (about 10 km) on both flanks of the ridge. Scarps which built these topographic highs face either toward the axis or away. Thus, the off-axis morphology appears as a set of horsts and grabens which could partly result from off-axis tectonic processes and/or from a shifting of the volcano-tectonic activity out of the axial valley during the last 3 Ma. Off-axis data show that serpentinized peridotites, more commonly observed on the western rift valley wall, crop out on the western flank up to 30 away from the axis. Models proposed to account for such rock exposure are usually related to the formation of the deep axial valley along slow-spreading ridges. Here, we propose that mantle rocks are exposed only in a very particular structural context which is directly controled by the ridge segmentation and is independent of the shape of the axial valley (symmetric or not). Serpentinites crop out within a V-shaped structure corresponding with the boundary between two adjacent segments, where seismic and gravity data reveal that the crust is thin and the lithosphere is thick. Here, the crust is fed by a lower magma supply than at the segment center (Snake Pit area). Thus, we interpret this segment end to be a region of extremely thin crust, where modest normal fault can bring mantle rocks to the surface.