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188292651 2007 set 7 complete skeletal

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Comparative Anatomy Notes Set 7
VERTEBRAE, RIBS, STERNUM, HETEROTOPIC BONES
- bones and bony armor in fish
- legacy
- dermal bony armor of ostracoderms
- bony scales in fish
- all constitute the exoskeleton of these animals
- also called dermal skeleton
- in head region, dermal armor arose from neural crest cells
- bones lying internal to skin = endoskeleton
- endoskeleton bones were at one time exoskeleton
- they sank from skin to reside as endoskeletal element
Ex. clavicle, nasal, frontal
- other endoskeletal elements like scapula, vertebrae, ribs, sternum, brain case (floor of skull), all
extremity bones - they were never part of dermal skeleton
- HOW WE KNOW THIS?
- all bone develops from mesenchyme
- can be head mesenchyme
- neural crest cells
- whether its head mesenchyme or sclerotome
-dermal or membrane bone = if bone arises directly from mesenchyme without
passing through cartilaginous intermediate stage
- exoskeleton
- replacement bone =bone arising from erosion of cartilage
- endoskeleton
Endoskeletal Tissues
- 2 categories
1. Visceral
2. Somatic
Visceral Skeleton - represented by those structures that operate gill chamber
- jaw cartilages and ear ossicles
- fish have weberian bones - ear ossicles
- derived from transverse processes of anterior most vertebrae of some
- they are not homologous to middle ear bone
Somatic Skeleton - all remaining internal bones that developed from mesoderm proper
- somite and scleratome
- subcategories
1. Axial Skeleton
2. Appendicular Skeleton
Development of vertebrae
- look at somite laterally
- remove dermatome
- morphogenesis
- posterior half separates and moves posteriorly
- anterior half separates and moves anteriorly
- anterior portion becomes posterior and posterior half becomes anterior
- myotome doesn’t move
- becomes intersegmental in position
- when scleratome gives rise to vertebrae , they lie intersegmentally
- vertebrae arise from splitting of scleratome
- just look at ribs
- ribs appear to be attached in between vertebrae

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Axial Skeleton Vertebrae
- can be cartilaginous or bony
- begin at occipital region of skull and terminate and tip of tail
- types of vertebrae based on structure of centrum
Acelous - centra that anterior and posterior surfaces are flat
- mammals
Amphicelous - concavities of anterior and posterior surfaces
- fish, primitive salamanders, Sphenodon, geckos
Procelous - concavity on anterior surface
- most reptiles
Opisthocelous - concavity on posterior surface
- most salamanders
Heterocelous - saddle-shaped
-neck of birds and turtles
Evolution of Vertebrae
- vert. of crossopterygians and labyrinthodont amphibians
- examine vertebrae of fossil records, there is a guide
- in transition from crossopterygians to labyrinthodonts, change led to lines of vertebrates
- occupation of land - adaptive radiation took place
- begins with primitive--rachitomous labyrinthodont vertebrae
- structure consists of 2 pleurocentra and U-shaped hypocentrum
- through time the hypocentrum is lost and pleurocentrum becomes larger and fuses to give rise to
centrum of modern amniote
HOW VERTEBRAE ARE GROUPED
- group the according to region of body
Fish - have 2 types
- trunk and tail vertebrae
Amphibians -
trunk - group of presacrals
- sacrals
- in presacrals - have dorsals and cervicals
- within dorsals - thoracics and lumbar
tail - have neural spine and hemal spine
- higher vertebrates don’t posses this
- hole going through hemal for blood vessels
Different regions
- Amphibians
- 1
st
vertebrates that possessed cervical vert.
- have 1
- caecilians -apodans
- have 200 or more vertebrae
- 1 cervical
- 1 sacral
- salamanders - dorsals
- Reptiles
- have atlas as 1
st
cervical
- axis - is 2
nd
cervical
- after that, variable number of cervical, dorsal, sacrals, and caudals
Ex. Turtle - 8 cervicals, 2 sacrals, 10 dorsals, 16-30 caudals
Snakes - all look alike
- in tail, no ribs, can see articulation points
- alligator - 8 cervicals, 11 thoracic, 5 lumbar, 2 sacrals, 40 caudals

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Comparative Anatomy Notes – Set 7 VERTEBRAE, RIBS, STERNUM, HETEROTOPIC BONES - bones and bony armor in fish - legacy - dermal bony armor of ostracoderms - bony scales in fish - all constitute the exoskeleton of these animals - also called dermal skeleton - in head region, dermal armor arose from neural crest cells - bones lying internal to skin = endoskeleton - endoskeleton bones were at one time exoskeleton - they sank from skin to reside as endoskeletal element Ex. clavicle, nasal, frontal - other endoskeletal elements like scapula, vertebrae, ribs, sternum, brain case (floor of skull), all extremity bones - they were never part of dermal skeleton - HOW WE KNOW THIS? - all bone develops from mesenchyme - can be head mesenchyme - neural crest cells - whether its head mesenchyme or sclerotome -dermal or membrane bone = if bone arises directly from mesenchyme without passing through cartilaginous intermediate stage - exoskeleton - replacement bone =bone arising from erosion of cartilage - endoskeleton Endoskeletal Tissues - 2 categories 1. Visceral 2. Somatic Visceral Skeleton - represented by those structures that operate gill chamber - jaw cartilages and ear ossicles - fish have weberian bones - ear ossicles - derived from transverse processes of anterior most vertebrae of some - they are not homologous to middle ear bone Somatic Skeleton - all remaining internal bones that developed from mesoderm proper - somite and scleratome - subcategories 1. Axial Skeleton 2. Appendi ...
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