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
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
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
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