Q: "Your post on ferret vertebra was wodnerful!  Would you do it for the
rest of the skeleton?"
 
You are asking a guy who collects, cleans, identifies (element, species,
sex, age, taphonomy, pathology), studies, measures, draws, photographs,
labels, and curates bones to TALK about them?  Are you crazy?  Do you
realize what you have caused??!!  How about I do it over several days to
minimize the trauma for those not so interested?
 
For ease of study, the ferret skeleton can be divided into two major
categories: the axial and the appendicular skeleton.  The axial skeleton is
composed of all the bones found along the body's axis, which include the
skull, mandibles, auditory ossicles, teeth, hyoid apparatus, vertebrae,
ribs and sternebrae.  The appendicular skeleton is basically everything
else, which includes the scapula and clavicle, the os coxae, the bones of
the thoracic and pelvic limbs, sesamoids, and genital bones.  Sometimes
dermal bones are present, such as in the armadillo, but since ferrets never
evolved them, they won't be discussed.  The sesamoids and genital bones are
actually part of the heterotrophic skeleton, which are bones that are not
associated with either the axial or appendicular bones, and include the os
cordis (a heart bone common in horses, cattle and other large ungulates),
the os rostrale (a rostral bone common in pigs, occasionally cows, and
other species), sesamoids (found inside muscle tendons and include the
patella and the fabella) and the os penis (baculum) and os clitoris.
However, for THIS discussion, I shall include the heterotrophic bones
within the appendicular skeleton (just be aware they are heterotrophic,
not appendicular).
 
Skeleton brachii: (Synonyms: thoracic limb, pectoral appendage, arm
skeleton).
 
Contrary to popular opinion, the ferret has a clavicle!  However, it is
usually cartilage or only partially ossified.  It is a rather small
(4-8 mm) "J"-shaped bone or cartilage rod, and is rarely present in
curated skeletons (it is usually lost during preparation).  If completely
or partially ossified, then it is clearly visible on X-ray.  While it has
little function in supporting the pelvic girdle (as does the clavicle in
humans), it does help support muscles in the neck and shoulder (which is
probably why it has been retained; it acts like a sort of sesamoid bone).
Clavicles are absent or diminished in carnivores to increase thoracic limb
mobility.  This is very important because it makes it easier for ferrets
to turn around in tight spaces, allows greater mobility in using the hands
and arms to obtain food, and increases the arc of movement in the front
limb.  This last reason is very important in a short-limbed creature like
the ferret because it allows for a greater stride in running.  I am unaware
of pathologies in the ferret clavicle, and have never heard of an instance
where it has been fractured.  (Synonyms: clavicle = clavicula, collarbone).
 
The scapula supports the thoracic limb, but unlike the pelvis, it is not
directly connected to the spine.  Instead, it is held in place with a
series of muscles, tendons and ligaments, which allow the scapula to freely
move with the appendage.  This increases stride and arc of movement, both
very important in short-limbed ferrets.  The blade of the scapula is
roughly shaped like a bee's wing, with a smooth oval area at the small end
where it connects to the humerus.  Scapular bone is very thin in ferrets,
and sometimes not all areas within the blade are completely ossified.
Even though the scapula is quite thin, it is typically protected from most
injury because it is heavily muscled on the top, which protects the bone
from most fractures.  I have only seen a single healed injury on a scapula;
a healed fracture of the acromion process.  However, I often find injuries
to the scapula in ferrets which died of trauma.  I suspect most injuries
which could seriously damage the scapula are usually terminal for ferrets.
It is possible cancerous growths could occur in the scapula, but I have
never seen one.  (Synonyms: scapula = shoulder blade, shovel bone).
 
The humerus in ferrets is fairly stout as a result of heavy neck, shoulder
and upper arm muscles.  I have seen large deltoid tuberosities in whole
males, but both the male and female ferret humerus show pronounced muscle
insertion scars.  Healed fractures of the humerus seem to be fairly rare
in ferrets; most I have seen are found in terminal trauma cases.  This is
probably because the energy required to fracture the humerus is sufficient
to damage the contents of the thoracic cavity and few ferrets survive.
In the three healed humeri fractures I have studied, all were distal, near
the condyle.  All were displaced spiral fractures which healed well, but
resulted in some degree of shortening or misalignment of the skeletal
element.  In one, the trochlea was heavily furrowed where the fracture had
passed through the joint, resulting in massive arthritis and reactive bone.
In a single case, a bone mass near the deltoid tuberosity was present,
which was approximately a centimeter in diameter.  Quite often, arthritic
lipping or the formation of bony projections can be found along the edges
of the head and trochlea in older ferrets, and occasionally you can see
scoring or furrowing on the articular surfaces of the trochlea.
(Synonyms: humerus = arm bone, clod bone).
 
In ferrets, the ulna is large, with a massive olecranon process, which
make sense considering the amount of digging done by polecats.  It has a
proximal and distal articulation with the radius, and both make up the
bones of the forearm.  Both bones slightly bowed, and are heavily muscled,
which gives the ferret Popeye forearms.  In ferrets, the radius and ulna
can easily cross over the other, which allows the ferret to turn their hand
palm-side up.  This allows the ferret great flexibility in manipulating
prey, digging, climbing, and making mischief, and makes their wrist and
hand bones structurally similar to bears, raccoons and humans.  I have
found a large number of healed fractures of the radius, ulna or both in
pet ferrets, which are probably a result of being stepped on or having
their arm caught in a door.  I have hypothesized that vets can identify
radioulnar injuries caused by a ferret being stepped on as opposed to those
from a swinging door by the following criteria: Stepping injuries = ulna
and/or radius broken midarm to distal with force progressing from cranial
to caudal; door injuries = ulna and/or radius broken randomly with
mediolateral force.  In three cases, the fractured radius and ulna fused
together.  In another case, the proximal radius healed as it if was
amputated and the distal portion fused to the ulna.  Arthritic lipping is
common in older ferrets along the proximal articular surfaces of both
bones.  Sometimes furrowing or scoring is present on the proximal articular
surfaces.  On rare occasion, reactive bone is seen at the elbow joint,
usually on the olecranon.  I have not seen a cancerous growth in the ulna
or radius, but suppose it is possible.
(Synonyms: ulna = elbow bone, funny bone; radius = radial bone)
 
The ferret has seven carpal bones and one sesamoid bone in the wrist, and
they are arranged like most other carnivores (PROXIMAL ROW: SCAPHOLUNATE =
os scapholunatum, os carpi intermedioradiale, radiointermediate, radial
carpal; TRIQUETRUM = os triquetrum, ulnar carpal, os carpi ulnare,
triangular, cuneiform; PISIFORM = accessory carpal, os carpi accessorium,
os pisiforme.  DISTAL ROW: TRAPEZIUM = C1, 1st carpal, os trapezium, os
carpale I; TRAPEZOID = C2, 2nd carpal, os trapezoideum, os carpale II;
CAPITATE = C3, 3rd carpal, os capitatum, os carpale III, magnum; HAMATE =
C4, 4th carpal, os hamatum, os carpale IV.  Medial Sesamoid = os
sesamoideum medialis).  I have seen two fractures of the ferret carpus;
both resulted in extensive fusion and formation of reactive bone tissue.
The bones form distinctive shapes and can be identified from each other,
BUT, those shapes have a moderate amount of variability, so identification
from position is preferable (especially of the distal carpals).  Sometimes
two (or on rare occasions, three) are naturally fused together.  Signs of
arthritis on the bones are rare, even in older ferrets.  Again, I have
never seen a cancerous growth in the wrist bones, but it is possible I
suppose.  (Synonyms: carpal bones = ossa carpi, wrist bones).
 
The ferret has five metacarpals in their palm, with two (rarely 3) palmar
sesamoids.  The metacarpals are numbered from 1 to 5, starting at the
thumb (1st metacarpal, MC1, os metacarpale I).  I have seen a lot of
healed fractures of the metacarpals, as well as a lot of reactive bone.
In several cases, two metacarpals have fused together midshaft.  In
another case, three metacarpals have fused at the proximal end.  There
are two small sesamoids between each metacarpal and first phalanx, which
are on rare occasion fused to the metacarpal (or the 1st phalanx).  Signs
of infection are not common, but not rare either.  I have never seen a
cancerous growth, but assume it can occur.
(Synonyms: metacarpus = hand bones, ossa metacarpalia, pastern bones,
rays).
 
The ferret has the same number of finger bones as humans; 2 on the thumb
and 3 on each finger; the third one is compressed mediolaterally to form
the support for the claw.  The phalanx closest to the metacarpal is the
proximal phalanx (= P1, 1st phalanx, phalanx proximalis, os compedale).
The middle bone is the medial phalanx (= P2, 2nd phalanx, phalanx media,
os coronale, middle phalanx).  The third bone, the one with the claw, is
the distal phalanx (= P3, 3rd phalanx, phalanx distalis, os unguiculare,
terminal phalanx, ungual bone).  "First phalanx" means the first bone past
the metacarpal, but which one?  There are various ways to distinguish this,
but I prefer "first phalanx third metacarpal." (P1MC3, first phalanx third
ray).  Ray is commonly used as a synonym for metacarpal (or metatarsal),
but I find the use of metacarpal allows immediate knowledge of the exact
location (if you say "right 1st phalanx, third ray", is it the hand or
foot?).  The proximal and medial phalanges are very similar in form to
humans, bear and raccoon, because the ferret, unlike the dog or cat, walks
on the entire foot (plantigrade).  The distal phalanges support the claws,
and are modified with a large ungual crest.  You can see this part of the
bone when the claw is torn off; it is the pink "quick" you see from the
side, through the claw (bone is VERY vascular, and tiny blood vessels run
under the bottom of the crest, which is why toe clipping can be used to
get blood samples).  Technically, the claw is the horny "fingernail" and
the bone is the distal phalanx; the phalanx is NOT the claw, but supports
it.  A pair of sesamoids are found between each metacarpal and the proximal
phalanx, and on occasion, some tiny ones can be found between the proximal
and medial phalanx.  I have seen a lot of broken and healed toes, lots of
reactive bone, and lots of minor arthritis.  I have never seen a bone
tumor.  (Synonyms: phalanges = finger bones).
 
Overall, I would say the most common pathologies (in order) are healed
fractures, arthritis, and reactive bone (generally results from infections
or inflammations).  I have seen very few bone masses (tumors/cancers) in
the thoracic limb skeleton.
 
Bob C
[Posted in FML issue 3478]