How to mount a hidden partition?

[joe at actionline.com]

joe wrote:
> Why does the mount syntax shown below fail to work
> to mount the named hidden partition on my system?
>
> brw-rw---- 1 root disk 8, 10 Jan 24 11:27 sda10
>
> mount -t ext4 /dev/sda10 /mnt/sda10

----------------
ET wrote:
> Pls show me the output of:
> cat /proc/partitions
>
> And the error message you get.
>
> There is no such a thing as a 'hidden partition'.

-----------------
The partition is "hidden" (to me) in the sense
that it does not appear when I use the command 'df'

Filesystem     1K-blocks     Used Available Use% Mounted on
/dev/sda5       15307020  4912896   9626124  34% /
udev             1020708       12   1020696   1% /dev
tmpfs             412276     1232    411044   1% /run
none                5120        0      5120   0% /run/lock
none             1030680       96   1030584   1% /run/shm
/dev/sda6       71559236 17893876  50081360  27% /home

# mount -t ext4 /dev/sda10 /mnt/sda10 ... returns this error message:

mount: mount point /mnt/sda10 does not exist

$ cat /proc/partitions
major minor #blocks name
 8  0  244198584 sda
 8  1     102400 sda1
 8  2   37280768 sda2
 8  3   26291384 sda3
 8  4          1 sda4
 8  5   15360000 sda5
 8  6   71680000 sda6
 8  7    3072000 sda7
 8  8   12586896 sda8
 8  9    4088511 sda9
 8 10   73722253 sda10
11  0    4399296 sr0