ANSWERS TO OBJECTIVES FOR BIO 3220 QUIZ 3
G. AXIAL SKELETON – THE SKULL AND VISCERAL SKELETON
7. Describe the dermatocranium and its origin. Name the four major categories
of dermatocranium bones. Identify prominent bones in these categories and approximate
their locations. (See Skull Handout.)
The dermatocranium consists of dermal bones that encase the chondrocranium and
splanchnocranium and contribute to the braincase, jaws, and skeletal elements
of the mouth (teeth). Phylogenetically, it is a membrane bone which probably
evolved from dermal armor.
The four major categories of dermatocranium bones are roofing bones, upper and
lower jaw bones, primary palatal bones, and opercular bones. Roofing bones include
nasal, frontal, parietal, orbit, and squamosal. Upper and lower jaw bones include,
premaxilla, maxilla, dentary, splenial, surangular, angular, coronoid, and prearticular.
Primary palatal bones include vomer, palatine, and pterygoid. (See handout for
approximate locations.)
8. Describe the splanchnocranium.
The splanchnocranium consists of visceral arches that support and move the gills
and contribute to production of the jaws in gnathostomes. In more advanced vertebrates,
parts of the splanchnocranium are modified to form derived structures such as
jaws, ears and parts of the hyoid apparatus and pharyngeal cartilage.
9. List the four main portions of a typical visceral arch. Name the portion
which may serve as a mid-ventral link of right and left arch.
Each arch, from dorsal to ventral, consists of cartilages or bars: pharyngobranchial,
epibranchial, ceratobranchial, hypobranchial, and (connecting right and left
sides) a series of basibranchial cartilages.
10. Discuss the evolutionary trends of visceral arches, including mandibular
arch and hyoid arch.
Visceral arches originally evolved to support the gills. This part of the skull
forms as cartilage and remains as cartilage in lampreys, sharks, and other cartilaginous
fishes. In bony fishes and tetrapods, most or all of the cartilage of the visceral
arches becomes ossified. The visceral arches play a key role in vertebrate evolution,
because the anterior visceral arches eventually evolved into the mandibular
arch and other parts of the splanchnocranium give rise to the hyoid apparatus
that supports the tongue and the trachea and larynx.
11. Describe the head (neurocranium, splanchnocranium, and dermatocranium)
of jawless vertebrates.
The chondrocranium, a cartilaginous neurocranium, protects the brain, otic,
and nasal organs. The splanchnocranium is present as a continuous visceral skeleton,
has a pharyngeal basket, and is branchial in function. The dermatocranium is
present as a dermal head skeleton and varies depending on group.
12. Describe the head (as above) of placoderms.
In placoderms, the chondrocranium is usually cartilaginous. The first arch of
the visceral skeleton, or splanchnocranium, form jaws. The dermal skeleton,
or dermatocranium included an armored head and thoracic shields.
13. Address the jaw suspension of placoderms.
The splanchnocranium exhibits autostylic suspension, having the mandibular arch
articulated directly to the cranium.
14. Address the jaw suspension of cartilaginous fish.
Primitive sharks exhibit amphistylic suspension, in which the second gill arch
(hyoid) plays no part in the suspension of the lower jaw. Most sharks exhibit
hyostylic suspenion, in which the upper jaw loses any major direct connection
with the braincase and the upper and lower jaws are supported solely by the
hyomandibula. Chimeras exhibit autostylic suspension, in which the upper jaw
(palatoquadrate) articulates or is fused with the chondrocranium, lower jaw
forms from the mandibular cartilage, and the jaw remains unsupported by the
hyomandibula.
16. Describe the head of bony fish.
The chondrocranium of early fishes was already well ossified, of dipnoans was
cartilaginous except exoccipitals, and of crossopterygians was somewhat cartilaginous
with a jointed braincase. The splanchnocranium, or visceral skeleton, exhibits
bone replacement instead of cartilage. The quadrate, or upper jaw, replaces
the palatoquadrate. The only replacement bone in lower jaw is the articular.
The second arch not branchial in function. The hyomandibula usually supports
jaw except in dipnoans with autostylic suspension. Ray-finned fish are hyostylic.
Crossopterygians are amphistylic. The splanchnocranium has branchial arches.
The dermatocranium, or dermal skeleton, includes a pectoral girdle joined to
skull and an operculum that covers the gills. Each major taxa has its own pattern
of dermal bones.
17. Describe the head of amphibians.
The heads of ancestral amphibians had nearly a full complement of replacement
bones with only the supraoccipital missing. Lissamphibians lack basioccipital
and basisphenoid and have paired occipital condyles (exoccipitals). In the visceral
skeleton, the quadrate articulates with the squamosal using autostylic suspension.
The hyomandibula became the ear ossicle (stapes or columella). The hyoid arch
elements support a large, fleshy tongue. The more posterior arches are generally
reduced to three, and also support tongue and larynx (hyoid apparatus). In the
dermatocranium, the operculum is lost, and the pectoral girdle is no longer
joined to the skull.
18. Examine the jaw suspension of tetrapods.
In tetrapods, the upper jaw alone suspends the lower jaw. This condition is
autostylic. This frees the hyomandibular of the hyoid arch from jaw suspension
and it is incorporated into the ear.
19. Describe the head of reptiles.
The neurocranium has a decreased number of bones, one occipital condyle and
is well ossified. The dermatocranium includes a full complement with some reduction
in roof bones, a temporal region, and a secondary palate. It exhibits cranial
kinesis. The splanchnocranium includes a quadrate with autostylic suspension,
an articular, a stapes, a hyoid apparatus, a larynx, and tracheal rings. Differences
occur in therapsids, having two occipital condyles, a synapsid skull, a free
quadrate and articular, and a squamosal and dentary that articulate.
20. Explain how anapsid, synapsid, euryapsid, and diapsids differ. Explain the
advantage of temporal fossae/fenestrae.
Anapsid - no temporal openings in the skull (turtles)
Euryapsid – one temporal opening bordered below by postorbital and squamosal
(plesiosaurs, ichthyosaurs).
Synapsid – one temporal opening bordered above by postorbital and squamosal
(mammals)
Diapsid – two temporal openings separated by postorbital and squamosal
(archosaurs, Sphenodon)
The presence of temporal fossae or fenestrae allows the passage of chewing muscles.
21. Characterize a secondary palate. List and advantages it provides.
Paired vomers merge, migrate posteriorly and dorsally, the parasphenoid is lost,
the pterygoids shorten, and shelf-like processes of maxillas and palatines grow
to midline in front of shifting nares to form secondary palate. The palate allows
simultaneous chewing and breathing.
22. Define cranial kinesis.
Cranial kinesis – movement between the upper jaw and braincase; provides
a way to change the size and configuration of the mouth rapidly; optimize biting
and rapid feeding.
23. How do therapsid heads differ from other reptiles? Why are these changes
significant?
Differences occur in therapsid heads, having two occipital condyles, a synapsid
skull, a free quadrate and articular, and a squamosal and dentary that articulate.
Throughout the Mesozoic era, there was a series of successive radiations of
therapsid reptiles, each of which tended to make a closer approach to the mammalian
condition than its predecessors. By the end of the Mesozoic, the changes developed
by this group had resulted in a form of body organisation that was typically
mammalian.
24. Describe the head of birds. Categorize it according to the number of temporal
fossae.
The neurocranium is larger, highly vaulted, incomplete dorsally, well ossified
and fused, with one occipital condyle. The dermatocranium has one big opening
as the supratemporal arch is lost, thus is it considered a modified diapsid.
The beak is comprised of the premaxilla and the dentary. It exhibits cranial
kinesis. The splanchnocranium is similar to that of reptiles.
25. Name the bones of the beak.
Premaxilla and dentary
26. Describe the head of mammals.
Neurocranium – larger, fusions, sutures, loss of bones, fontanels, sinuses,
two occipital condyles
Dermatocranium – nasal structures with conchae, tympanic bulla, malleus,
squamosal articulation with dentary bone, synapsid, decreased number of bones
Splanchnocranium – quadrate becomes incus, articular becomes malleus ,
hyomandibula previously evolved to become the stapes
27. Identify any unique changes to the mammalian skull.
Certain bones tend to fuse: postparietal with supraoccipital, basioccipital
with exoccipitals, otic bones with squamosal (temporal), four sphenoid bones
into one sphenoid.
Bones not found in mammals include: prefrontals, postfrontals, postorbitals,
quadratojugals, parasphenoid.
All other dermal bones of lower jaw have been lost except the angular, prearticular,
and articular, which have shifted away from lower jaw.
28. Describe the articulation between the upper and lower jaws in mammals.
In mammals, the dentary bone (mandible), the only bone in the lower jaw, articulates
with the squamosal bone (part of temporal bone). No longer needed with this
new jaw articulation, the articular and quadrate bones migrate into the middle
ear to become the malleus and incus respectively, two of the three mammalian
ear ossicles that conduct sound from the tympanic membrane to the inner ear.
29. Name the sole mammalian lower jaw bone.
Dentary bone
30. Categorize the mammalian skull according to the temporal fossae.
Synapsid – one temporal opening with an infratemporal = zygomatic arch
31. Define suture, fontanel, paranasal sinus, conchae, turbinate, and tympanic
bulla.
Suture – the line of junction or an immovable joint between two bones,
especially of the skull
Paranasal sinus – any of the paired cavities, designated frontal, sphenoidal,
maxillary, and ethmoidal, located in the bones of the face and lined by a mucous
membrane continuous with that of the nasal cavity
Conchae – cartilaginous or slightly ossified scrolls that occupy the major
portion of each half of the nasal cavity and are covered with nasal mucosa
Turbinate – a bone situated along the side wall of the nasal cavity covered
by mucous membrane
Tympanic bulla – round bone that encloses the middle ear
32. Trace the evolution of the visceral arches and their derivatives. See Handout.
About 100 pairs of gill slits in some protochordates, about 5 to 15 pairs in
early vertebrates, about 6 pairs in most jawed vertebrates.
In jawless vertebrates, gill bars not jointed. Gnathostomes had jointed visceral
arches; usually 4 paired segments per arch. First visceral arch enlarges to
become jaws, mandibular arch. Epibranchial forms upper jaw and is called the
palatoquadrate. Ceratobranchial forms lower jaw and becomes the mandibular cartilage.
Second visceral arch becomes the hyoid arch. Epibranchial becomes hyomandibula.
Succeeding arches become branchial arches.
33. Define columella, stapes, malleus, incus, larynx, and hyoid apparatus.
Columella – a rod-like bone (ossicle) that picks up sound vibrations from
the eardrum and transmits them to a membranous oval window in the inner ear;
rudimentary stapes
Stapes – a stirrup-shaped small bone or ossicle in the middle ear which
attaches the incus to the inner ear
Malleus – a hammer-shaped small bone or ossicle of the middle ear which
connects with the incus and is attached to the inner surface of the eardrum
Incus – an anvil-shaped small bone or ossicle in the middle ear that connects
the malleus to the stapes
Larynx – an organ in the neck of mammals involved in control of breathing,
protection of the airway and sound production
Hyoid apparatus – an articulation of bones that acts to suspend the tongue
and the larynx beneath the skull
34. Discuss some evolutionary trends of the skull.
Throughout human evolution there has been a tendency to change skull proportions
in two ways: first to increase the size of the brain and second to decrease
the size of the jaws, jaw muscles and teeth. This has changed the overall shape
of the skull: taken together these changes produce a taller skull, with fewer
ridges for muscle attachment and a shorter retrousse face. The position of the
foramen magnum has also changed, decreasing the need for powerful neck muscles.
Also, there has been a decrease in the number of bones and in the number of
visceral arches.
H. APPENDICULAR SKELETON
1. Describe the formation of the bones of the appendicular skeleton.
During embryonic development, the skeleton remains primarily cartilaginous to
form the basic structural components and framework of the body. After the basic
structure of the embryo is formed, bone begins to be deposited in two ways.
Membrane/dermal bone, also called intramembranous or dermal bone, is formed
through the deposition of calcium salts and osteoblasts within the connective
tissue near skin surfaces. Cartilage replacement bone is formed in and around
the cartilage of the embryonic endoskeleton. The embryonic endoskeleton forms
the basic structure of the skeletal system. The appendicular skeleton includes
the pectoral girdle (shoulder), pelvic girdle (hips), and the bones attached
to them (arms and hands, legs and feet).
2. Identify the function of the pectoral girdle.
The function of the pectoral girdle is for attachment of the pectoral appendages.
3. Name the replacement bones of the pectoral girdle.
Coracoid, scapula, suprascapula
4. Name the membrane bones of the pectoral girdle.
Clavicle, cleithrum, supracleithrum, postcleithrum, posttemporal, interclavicle,
episternum
5. Discuss the phylogenetic tendencies of these replacement and membrane bones.
Dermal (membrane) bones dominate in the pectoral girdle of bony fishes, whereas
replacement bones predominate in tetrapods.
6. Identify the part of the pectoral girdle that articulates with limbs or
fins.
Limbs and fins articulate with the scapula at the glenoid fossa.
7. Distiguish the pectoral girdle of all vertebrate classes.
Cartilaginous fish – completely cartilage; dermal elements are absent;
made up of the coracoid, scapula, and suprascapula; not connected to axial skeleton
Bony fish – membrane (dermal bones) are most prevalent; made up of the
cleithrum, supracleithrum, postcleithrum; posstemporal anchors to skull; coracoid
and scapula are replacement bones
Amphibians – membrane bones are reduced; posttemporal is lost; gain clavicle
as internal brace; coracoid, scapula, suprascapula are replacement bones; urodeles
have no membrane bones, no clavicle; anurans have clavicle, lack interclavicle,
usually lack cleithrum
Reptiles – Most have scapula, coracoid, some have clavicle and interclavicle,
lizards are only group with significant clavicle.
Stem reptiles and synapsids – many membrane bones present; most replacement
bones present; new posterior coracoid
Modern reptiles – have scapula, coracoid, sometimes a clavicle, sometimes
an interclavicle
Crocodiles – clavicle decreased or absent
Turtles – have acromion process; clavicle fused with shell
Snakes – have no girdle
Lizards – only group with significant clavicle
Birds – furcula is formed from two clavicles and interclavicle; scapula
is blade like and parallel to the spine; coracoid articulates with the sternum
Mammals – clavicle only membrane bone retained (but not in all mammals);
anterior coracoid lost; posterior coracoid forms coracoid process on scapula;
scapula is unique in having a spine that continues ventrally as acromion process;
neither procoracoid or coracoid present in eutherian mammals except for a vestige,
the coracoid process of the scapula that is above the glenoid fossa
8. Identify the unique role of the posttemporal bone.
The posttemporal bone may bear spination and anchors to the skull. It links
the girdle with the dermatocranium.
9. Explain the difference between the anterior and posterior coracoids and
the coracoid process.
The original coracoid is anterior, and posterior to this a new ossification
center originated giving rise to the posterior coracoid. In therian mammals,
the anterior coracoid is lost and the posterior coracoid fuses with the scapula
creating the coracoid process.
10. Name the bone with an acromion process. A gleniod fossa?
The scapula is unique in having a spine that continues ventrally as the acromion
process. Also, the coracoid process of the scapula is above the glenoid fossa.
11. Identify the function of the pelvic girdle.
The function of the pelvic girdle is for attachment of the pelvic appendages.
Also, it supports the weight of the body from the vertebral column. It also
protects and supports the lower organs, including the urinary bladder, the reproductive
organs, and the developing fetus in a pregnant woman.
12. Name the bones that comprise the pelvic girdle. What type of bones are
these?
The Pelvic Girdle, also called the hip girdle, is composed to two coxal (hip)
bones. The coxal bones are also called the os coxae or innominate bones. During
childhood, each coxal bone consists of three separate parts: the ilium, the
ischium, and the pubis. In an adult, these three bones are firmly fused into
a single bone. They are replacement, endochondral bones.
13. Name the socket for the thigh bone. Define innominate, coxal, symphysis,
and pelvic cavity.
The acetabulum is the socket for the thigh bone.
Innominate bone – the great bone which makes a lateral half of the pelvis
in mammals; hip bone; haunch bone; huckle bone. It is composed of three bones,
ilium, ischium, and pubis, consolidated into one in the adult, though separate
in the fetus, as also in many adult reptiles and amphibians
Coxal – the hip or hip joint
Symphysis – a growing together of bones originally separate, as of the
two pubic bones
Pelvic cavity – the space bounded by the bones of the pelvis and containing
the pelvic viscera
14. Characterize the pelvic girdle for all vertebrate classes.
Pelvic girdles of fishes – weakly supported by a single skeletal element
on each side of the body (plates); these elements usually separate but may articulate
with each other (pelvic symphysis) or be joined by a bridge of cartilage (cartilaginous
fishes).
Pelvic girdles of tetrapods – 3 bones are constant in adult; embryos develop
cartilaginous pelvic plate that ossifies at two centers: anterior pubis and
posterior ischium; dorsal to pelvic plate gives rise to the ilium; at the junction
of the ilium, pubis, and ischium, a socket forms that accommodates the head
of the femur (acetabulum); pelvic symphysis; dorsally, ilium is braced against
transverse processes of one or more sacral vertebrae; in amniotes, the sacrum
and girdle are often rigidly united and form the pelvis
Primitive amphibians – solid triangle-shaped girdle; pubis with obturator
foramen; pubis of modern amphibians is cartilaginous; one sacral vertebra
Reptiles – variable, but basically like labyrinthodonts; firmer contact
with spine; puboischiadic fenestrum usually present (also called ischiopubic);
two sacral vertebrae
Birds – ilium and ischium greatly expanded and united with the synsacrum;
no pelvic symphysis; usually three sacral vertebrae
Mammals – long and expanded ilium which extends forward from acetabulum;
large obturator fenestrum represents both the obturator foramen and the puboischiadic
fenestrum of the ancestor; a symphysis almost always present; this may be a
pubic symphysis; usually three sacral vertebrae; monotremes and marsupials have
epipubic bones that articulate with pubic bones and may serve to support the
marsupium; ilium, ischium, and pubis ankylose to form a left and right innominate
bone
15. Describe the function and structure of fins.
The function of fins is for steering, rolling, braking, stabilizing, and to
provide forward and vertical movement. Each fin is supported within body by
a series of pterygiophores (radials); proximal piece often called a basal. There
is a skeletal base that may be cartilaginous or bony. Fins of advanced fishes
supported by a series of fin rays. Rays are covered with skin.
16. Define lepidotrichia, ceratotrichia, pterygiophore, basals, and radials.
Lepidotrichia – segmented, bony dermal scales
Ceratotrichia – cartilaginous, unsegmented fin support structures
Pterygiophore – the bones or cartilages with which the base of the rays
of the median fins articulate; the connecting points for the dorsal and anal
fin rays
Basal pterygiophores are the proximal elements. Radial pterygiophores are the
more distal elements.
17. Describe paired fins in all classes that have them.
Agnathan vertebrates – no trace of paired appendages
Placoderms and acanthodians – varied from stiff spines to hinged arms
and multiple spines
Class Chondrichthyes – relative importance of dermal and cartilaginous
skeleton was reversed, the latter dominating the former; internal skeleton with
series of radials with heavy basals; if there are 3 basals: pro, meso, and metapterygia
Class Actinopterygii – proximal row of bony radials and distal series
of lepidotichs
Class Sarcopterygii – archipterygium (dipnoans) have radials that are
biserial, series of radials on each side of a median axis; crossopterygium have
radials that are uniserial, series of radials on one side of the axis, ancestral
to tetrapod limb.
18. Discuss the location, function and variations of median fins.
The median fins, or dorsal and anal fins, function in rolling, defense, and
display. They are located along the centerline, dorsally and ventrally. There
are many variations of median fins between classes, including size, shape, and
color.
19. Address the different arrangements of caudal fins, specifically heterocercal,
hypocercal, diphycercal and homocercal.
Caudal fins may be one of several shapes.
Diphycercal – spine straight to tip of tail; dorsal and ventral lobes
about equal
Heterocercal – spine tilts upward; dorsal lobe longer
Hypocercal – spine enters a larger ventral lobe
Homocercal – all of fin membrane posterior to spine; dorsal and ventral
lobes about equal
20. Discuss the origin of tetrapod limbs.
One theory exists, though it is usually not accepted, that fishes evolved in
times of drought and used limbs to move between ponds. Another theory is that
tetrapods evolved in humid areas. They walked on the bottom with their lobe-shaped
fins and could crawl up on damp shores to escape enemies and to find food. Limbs
evolved from a crossopterygium. Homologies have been established between the
proximal segments of fin axis and the proximal limb bones.
21. Depict the function and evolutionary trends of limbs.
Without the evolution of paired appendages and specialized girdles to attach
them to the backbone, it is unlikely that any vertebrates would have emerged
onto land and evolved tetrapod modes of locomotion. In all living fishes, the
pelvic girdle is detached from the vertebral column. In sharks, they are imbedded
in the trunk musculature. In many derived bony fishes, the pelvic fins have
moved far forward of their original position and in many cases, are fuses to
the pectoral girdle. Tetrapods evolved from a lineage of bony fishes called
the lobe-finned fishes, which retained the ancestral position of the pelvic
girdle and fins at the back end of the body, allowing for the eventual evolution
of the tetrapod limbs, with two in front and two in back. In more derived tetrapods,
the birds and mammals, the major innovation of the appendicular skeleton has
been to move the legs directly underneath the body, rather than being sprawled
out to the side, as in most reptiles.
22. Describe the structure of pectoral and pelvic limbs including propodium,
epipodium, mesopodium, metapodium, and phalanges.
Tetrapod limb is divided into segments: the propodium – humerus (upper
arm) and femur (thigh); the epipodium (forearm or shank) – radius (medial)
and ulna (lateral), tibia (anterior) and fibula (posterior); the mesopodium
– carpals (wrist) and tarsals (ankle); the metapodium – metacarpals
(palm) and metatarsals (instep); phalanges (digits)
23. Define manus and pes. Define epiphysis and diaphysis.
Manus – forefoot; mesopodium, metapodium, phalanges
Pes – hindfoot; mesopodium, metapodium, phalanges
Epiphysis – the end of a long, initially separated from the main bone
by a layer of cartilage that eventually ossifies so the parts become fused
Diaphysis – the main midsection (shaft) of a long bone; ossifying shaft
24. Explain long bone growth in terms of length and diameter.
A long bone, such as your femur (thigh bone), grows in length at either end
in regions called growth plates. Growth occurs when cartilage cells divide and
increase in number in these growth plates. These new cartilage cells push older,
larger cartilage cells towards the middle of a bone. Eventually, these older
cartilage cells die and the space they occupied is replaced with bone. When
a bone has reached its full size, its growth plates are converted into bone.
Diameter growth occurs by the action of osteoblasts located at the periphery
of the bone and osteoclasts located lining the marrow cavity.
25. Discuss variations of limbs in tetrapod classes.
Amphibians (other than Gymnophiona)
Limbs splayed to sides of body
Epiphyses of hyaline cartilage
Salamanders--fit like corks into the ends of bony shafts.
Anurans--calcified and fit over the ends of the shafts like match sticks.
Podials often cartilaginous
Principal joint of foot is between the podials and metapodials
Usually 4 digits on hand, 4-5 on hind foot
1-3 phalanges in each toe
Marrow cavities of long bones of amphibians and higher vertebrates (but not
fishes) produce blood cells
Reptiles
Most have limbs far to the side of body
Epiphyses usually cartilaginous
An extra bone (pisiform) may be added to outside of carpus
Tibiale no longer free bone in tarsus
Joint of foot is often between podials
Generalized phalangeal formula – Manus: 2-3-4-5-3; Pes: 2-3-4-5-4
Birds
Epiphyses cartilaginous in immature birds; virtually absent in adults.
Principle digit of wing is number 2 or 3.
Generalized phalangeal formula: 2-3-4-5-0
Mammals
Have bony epiphyses on each end of the long bones, distal ends of the metapodials,
and proximal ends of all by the terminal phalanges
Pisiform is retained
In tarsus, the fibulare forms the heel bone (calcaneus)
Tibiale joins the intermedium and the resultant large bone, called the astragalus
(talus), lies partly over the calcaneum
The ankle joint is between the astragalus and tibia
Basic phalangeal formula: 2-3-3-3-3