Next, in vivo images of a mouse tail were obtained with WS-OCT. A mouse of the same type used in the ex vivo study was anesthetized using the same procedures. A photograph of the mouse under imaging and micrographs of a tail section slice of after hematoxylin and eosin (H&E) stain are shown in Fig. 3(a). Twenty min after the anesthetic injection, three different locations on the distal end of the mouse tail were imaged. The reduced scattering coefficient of the tail tissue was measured as . The experimental results are shown in Fig. 3. For all locations, WS-OCT showed a significantly improved penetration depth and SNR. In particular, multiple-layered structures were visualized with WS-OCT: the double-layered structure at location 1 [Fig. 3(b)] and the triple-layered structures at locations 2 and 3 [Figs. 3(g) and 3(l)] as indicated by gray arrows (note the difference in scales between locations 1, 2, and 3). The shapes and locations of these structures correspond to epidermis, connective tissue textures, and sebaceous glands. However, the uncontrolled beam and the spatial compounding method only visualized the most superficial single layer at all locations. The average depth profiles for 15 A-scans are plotted for each location in Figs. 3(f), 3(k), and 3(q). The enhancement factors for the first layer were 5.26, 6.88, and 6.06 at locations 1, 2, and 3, respectively. These enhancement factors are comparable to that of the former ex vivo experiments implying that the efficiency of wavefront shaping is not severely degraded in in vivo environments. The enhancement factors at the second peaks were 4.47 for location 1 and 3.97 for location 2, slight smaller than those of the first layers. Notably, the enhancement factor decreases as the depth increases. This may be because the fraction of uncollected light will increase as the depth of the scatters increases. At location 3, although the intensity level of the second peak [Fig. 3(q), the orange arrow] is much smaller than that of the other locations, an enhancement factor of 3.36 is still comparable to the other locations which implies the enhancement does not depend on the absolute level of intensity.