Q: "Can you explain the skull picture a bit better?  Not just the part
    about smell, but more about the entire [skull]?"
 
A: At first I was not going to answer this question because the anatomy
of the skull has really little to do with the enrichment posts other
than the brief mention I made to illustrate the importance of smell to
the ferret (and later, for hearing).  The POINT was that the sense of
smell in the ferret was extremely important, which is why the photo only
had minimal information presented: "here's the skull, these areas are
dedicated to smell, they make up about a third of the skull volume,
smell is important."  If you think the enrichment series was long,
entire series of books have been published on skulls and brain anatomy
and structure.  I could easily match the size of the enrichment series
talking about the ferret brain alone, doubling or tripling it when
discussing the skull.  Nonetheless, understanding the reasons why
enrichment is important goes a long way in convincing people to spend
more time increasing a ferret's quality of life, so answering the
question has value.  To understand this post, I suggest you open the
accompanying photo in a separate link, or perhaps print it out for easy
reference.  This photo is identical to the last one, except that in
this republishing effort I have placed reference numbers so I don't have
to waste time and space describing locations.
 
http://homepage.mac.com/billgruber/fml/skullq.html
 
(1) The inside view of the lower right jaw (mandible): you will note the
teeth form a shark-like sawtooth pattern designed to consume an all-meat
diet.  The mandible is locked to the skull, preventing chewing motions,
only allowing an up-and-down shearing movement that cuts food into small
pieces.
 
(2) You should also notice the lower molar (M1), which is peg-like and
does not come into direct contact with the teeth of the upper jaw
(maxilla).  This tooth is either in the process of being lost, or it is
only being maintained to help crack insect carapaces, snail shells, and
small bones (working like a nut cracker).  In either case, it is quite
small and barely erupts above the gum line.
 
(3) The floor of the cranial cavity (cranial vault).
 
(4) The large, inflated auditory bulla, evidence of enhanced hearing in
the ferret.
 
(5) The occipital condyle that connects (articulates) the skull to the
spine (vertebral column); the comparatively large size supports a heavy
skull balanced on a long neck that is covered with massive muscles.
 
(6) The flared and squared-off rear of the skull (nuchal crest), which
allows for strong attachment of powerful neck muscles.
 
(7) The ridge of bone (sagittal crest) running along the top of the skull
is a strong attachment for powerful chewing muscles; the small size of
this crest is evidence of gender (female).
 
(8) The interior of the cranial cavity or cranial vault (colored pink),
the shadowy lines mark the locations of the convolutions of the brain,
showing the ferret brain to be morphologically complex at the macro
scale.
 
(9) The region of the olfactory bulb and associated structures (colored
blue).  They are housed in the most frontward part of the cranial cavity
(at the rostral boundary) immediately adjacent to a thin sheet of bone
(ethmoid) that separates the interior of the nose (the nasal cavity)
from the cranial cavity.  The comparatively large size of this region is
evidence of the importance of odor to the ferret.
 
(10) The frontal bones in many species contain large openings, or
sinuses, filled with mucous membranes.  Sinuses are hypothesized to serve
many functions, most notably reducing the weight of the skull.  Because
of the inflated nature of the nasal cavity, the frontal bones in the
ferret are thin-walled and lack significant sinus spaces.  While the
ferret skull generally HAS a frontal sinus (as well as other minor
sinuses), for the most part the sinus is diminutive, and in some skulls,
nonexistent.
 
(11) The sieve-like cribriform plate (part of the ethmoid bone) is
perforated with scores of tiny holes that allow the passage of olfactory
nerves from the nasal cavity.  Compared to other mammals, this region is
proportionately quite large, additional evidence of the importance of
smell to the ferret.
 
(12) The nasal cavity (colored orange) serves two basic functions; it
is the beginning of the respiratory tract, warming and moistening air
before it enters the lungs, and it protects the nasal mucosa (a type of
mucous-producing skin (epithelium) that is rich in blood and olfactory
nerves).  The front part of the nasal cavity is inflated and rounded like
a balloon to create the largest space possible so it can hold the maximum
amount of nasal mucosa.  In the ferret, the nasal cavity is packed with
thin-walled, labyrinthine bones called nasal turbinates (nasal conchae)
that support the nasal mucosa, serving to tremendously increase the
surface area.  The nasal cavity is roughly a third the size of the skull,
proportionately quite large compared to other animals, and is crammed
with nasal turbinates covered with olfactory nerve-rich nasal mucosa: it
is the nose of an animal that uses scent in the same way humans use
sight.
 
(13) The nasal vestibule is the opening into the nasal cavity.  It is
quite large, allowing for relatively large quantities of air to be
exchanged.  This not only provides the oxidant to burn the fuels of the
body, but also to allow large amounts of air to circulate within the
nasal cavity, increasing the chance that rare odors will be detected.
 
(14) The choana, the opening from the nasal cavity to the nasopharynx,
is relatively small compared to the overall size of the nasal cavity.
Like a funnel, the small size of the choana forces much of the air to
"stagnate" (recirculate) within the nasal cavity, which not only
increases its warmth and moisture before going into the lungs, but also
allows the air to saturate the mucous membranes, increasing the chance
of detecting rare odors.
 
Bob C
[Posted in FML issue 4233]