Exam 2 - Body Skeleton

Question 1

Vertebrae

Answer 1

1. First stage
2. Second stage
3. Projections from centra

Question 2

First stage (vertebrae)

Answer 2

i. Dorsal arches
a. Neural arches
b. Interneural arches - protects nerve chord
ii. Ventral arches
a. Hemal arches
b. Interhemal arches

Question 3

Second stage

Answer 3

i. The formation of centra composed of an intercentrum and pleurocentrum
ii. The bases of the ventral arches expand to form the centra
iii. Centra anchor and support the arches

Question 4

Projecting from the centra are:

Answer 4

i. Apophyses ‒ articulation surfaces
a. Diapophyses and parapophyses ‒ articulation points for the ribs
b. Zygapophyses ‒ articulation points between vertebrae
ii. Transverse processes

Question 5

General structure of vertebrae: Amphicoelous

Answer 5

i. Centrum is concave on both ends
ii. Limited motion in any direction
iii. Space between is filled with cartilage or the remains of the notochord
iv. Fishes, some salamanders, primitive lizards (geckos)

Question 6

General structure of vertebrae: Opisthocoelous

Answer 6

i. Convex anteriorly and concave posteriorly
ii. Motion in any direction except as limited by the zygapophyses
iii. Do not dislocate easily
iv. Some salamanders

Question 7

General structure of vertebrae: Procoelous

Answer 7

i. Concave anteriorly and convex posteriorly (ball-and-socket joint)
ii. Anurans and modern reptiles

Question 8

General structure of vertebrae: Acoelous

Answer 8

i. Centra have flat ends
ii. Able to withstand compression
iii. Limited motion
iv. Mammals

Question 9

General structure of vertebrae: Heterocoelous

Answer 9

i. Saddle-shaped ends
ii. Prevent rotation around the axis of the spine
iii. Enables lateral and dorsoventral flexion of the neck
iv. Birds

Question 10

Ribs

Answer 10

1. Are struts that articulate or fuse with ribs
2. Function to:
   i. Anchor muscles
   ii. Form a protective cage around the body iii. Suspend organs within the body
   iv. Accessory breathing structure

Question 11

Fish ribs

Answer 11

have two sets of ribs on every segment

i. Dorsal ribs
ii. Ventral ribs

Question 12

Primitive tetrapod ribs

Answer 12

had two headed ribs

Question 13

Basic types of rib

Answer 13

Basic types of ribs

i. True ribs - attaches to the sternum
ii. False ribs - attaches to the costal cartilage that then attaches to the true ribs
iii. Floating ribs - not attached
iv. Spare ribs and short ribs

Question 14

Uncinate processes

Answer 14

i. Project posteriorly from the ribs in the anterior portion of the body
ii. Found in birds, a few reptiles, fossil reptiles and early amphibians

Question 15

Sternum

Answer 15

1. Functions as the origin for chest muscles
2. Also attaches to true ribs
3. Lacking in fish
4. Lacking in ancestral amphibians but found in extant ones
5. Also lacking in turtles
6. Secondarily lost in snakes and legless lizards
7. Found in most lizards and mammals and all birds
8. Thought to have arose independently several times from midventral connective tissue

Question 16

Notochord

Answer 16

1. Functions to stiffen body (helps with forward propulsion in swimming)
2. Almost all early vertebrates had a notochord with neural and hemal arches

Question 17

Evolution of spine in advance fishes

Answer 17

Next step was for the notochord to be interrupted by centra and with far more elaborate arches and processes
2. Increases strength of the spines and provided places for muscle attachment

Question 18

Bony fishes have:

Answer 18

i. Centrum
ii. Neural arch with spine
iii. Hemal arch with a spine in the tail

Little regional differentiation

i. Two regions
ii. Trunk regions - has ribs
iii. Caudal region - has hemal arch and no ribs
iv. First vertebrate modified to articulate with the skull

Question 19

• Subclass Chondrostei (sturgeon, paddlefish)

Answer 19

i. Notochord is present
ii. Vertebrae secondarily cartilaginous
iii. Neural and interneural arches are present above
iv. Prominent neutrals spine
v. Possess ventral arches and ribs attached

Question 20

Bowfin (Amia Calva) and teleosts

Answer 20

i. Vertebrae ossified
ii. Centra begin to replace the notochord as the primary body support
iii. Neural spines are present

Question 21

Sarcopterygians

Answer 21

. Notochord still is the primary supportive element

ii. Rudimentary and cartilaginous in extant species
iii. Stem groups had three elements: neural arch, intercentrum, and paired pleorocentra

Question 22

How did terrestrial environment modifiend the spine of amphibians?

Answer 22

i. Modified to withstand the force of gravity
ii. No need to resist stress of axial muscles
iii. Paired appendages had to support the body and transmit stress to the spine
iv. Resist bending in some regions and be flexible in others

Question 23

New requirements for amphibians

Answer 23

i. Firm centra
ii. Intervertebral joints
iii. Processes
iv. Closer relationship with the limb girdles

Question 24

Early amphibians vertebrae were similar to the crossopterygians how?

Answer 24

i. Notochord was persistent
ii. Large intercentrum circling the notochord
iii. Small paired pleurocentra
iv. Neural arch

Question 25

Modern amphibians are highly modified how?

Answer 25

i. Have zygapophyses
ii. Cervical vertebrae articulate with the skull and have reduced ribs (first time to see a true atlas)
iii. Trunk vertebrae have ribs but not in anurans
iv. Single sacral vertebrae
v. Caudal vertebrae lack zygapophyses and have hemal arch
vi. Anurans have no free caudal vertebrae, are fused into the urostyle (urostyle is the fused caudal vertebrae of
an Anuran) (caudal vertebrae is posterior to the pelvic girdle in frogs)

Question 26

Amniotes

Answer 26

1. Centrum of group is called an intercentra
2. Have strong zygapophyses except in tail
3. First two vertebrae are modified to support the skull

Question 27

Reptiles:

Answer 27

i. Very distinct cervical vertebrae
ii. Two or more sacra vertebrae
iii. Hemal arches are no separate elements called chevron bones

Question 28

Birds

Answer 28

i. Vertebral column is more uniform than most tetrapods
ii. Have more cervical vertebrae
a. 12 usually, swans have 24
b. Enables some to turn the head 180 degrees
iii. Synsacrum is the fusion of the thoracic, lumbar, and first few caudal vertebrae and the ribs
iv. Synsacrum fuses to pelvic girdles

Question 29

Mammals

Answer 29

i. Seven cervical vertebrae
ii. About 20 trunk vertebrae iii. Three more sacral vertebrae fused into sacrum
iv. Caudal vertebrae, some chevron bones at the base of the tail

Question 30

Cranio-vertebral joint

Answer 30

1. Amphibians first vertebrate to have a neck
2. Reptiles and birds have a ball-and-socket joint
   i. Vertebrae now called atlas
   ii. Second vertebrae modified and called axis
   a. Present in some reptiles
   b. Developed in the synapsid line
3. Mammals have both the atlas and the axis

Question 31

Atlas

Answer 31

i. Atlas has: (yes)
a. Large zygapophyses
b. Large transverse processes
c. Hardly any centrum
d. All of these permits up and down motion

Question 32

Axis

Answer 32

Axis has: (no)

a. Large neural spine
b. Large centrum
c. Permits side to side movement and rotation around the axis of the spine

Question 33

Vertebral modifications

Answer 33

1. Direction of the neural spine
   i. Oriented so that its long axis is parallel to the forces imposed by the axial muscles
   ii. Result is the spine experiences compressive forces rather than shear forces
2. Height of the neural spine
   i. Height is proportional to the mechanical leverage that the muscles exert to move or stabilize the vertebral
   column
   ii. Acts to transfer the force of muscle contractions to the centra
   iii. To increase force, need to enlarge both the muscle and its attachment. This yields a longer spine