As described in Chapter 6, the skeleton is divided into axial and appendicular portions (see Figures 6.1 and 7.1). The axial skeleton is structured from 80 bones segregated intothree major regions: the skull, vertebral column, and thoraciccage (Figure 7.1) . This part of the skeleton (1) forms the lon-gitudinal axis of the body, (2) supports the head, neck, and Chapter 7 The Skeleton 199 7 Figure 7.1 The human skeleton.
Above: Some cameras have a switch to set it to auto or manual focus. Manual focus, meanwhile, disables autofocus and enables you to adjust it yourself. This is useful when the focusing system can't find focus for whatever reason, such as when it's too dark or when there's little contrast in the scene.
The lenses that have the built-in focusing motor have the designation AF-S, which stands for Auto Focus-Silent Wave Motor. Lenses that do not have this built-in motor cannot autofocus on the D3300 and D5300 camera bodies. Many, but not all, of the Nikon lenses have a switch on the camera barrel that allows you to switch between manual focus and autofocus. This switch is labeled with M/A and M. In the M/A mode, the camera tries to autofocus as long as the camera is set to autofocus.