def atlas_slice(atlas, slice_number):
    """
    A function that pulls the data for a specific atlas slice.

    Parameters
    ----------
    atlas: nrrd
        Atlas segmentation file that has a stack of slices.

    slice_number: int
        The number in the slice that corresponds to the fixed image
        for registration.

    Returns
    -------
    sagittal: array
        Sagittal view being pulled from the atlas.

    coronal: array
        Coronal view being pulled from the atlas.

    horizontal: arrary
        Horizontal view being pulled from the atlas.

    """
    epi_img_data2 = atlas.get_fdata()
    sagittal = epi_img_data2[140, :, :]
    coronal = epi_img_data2[:, slice_number, :]
    horizontal = epi_img_data2[:, :, 100]
    return sagittal, coronal, horizontal