Comparative Anatomy
Bone
Note Set 7
Chapters 7, 8, & 9
Bone Legacy

Exoskeleton or dermal skeleton
Dermal bony armor of ostracoderms
 Bony scales in ancient fish


Cranial dermal armor arose from neural crest cells

Endoskeleton
Internal to skin
 Where once exoskeleton


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Ex: clavicle, nasal, frontal, and parietal bone
Other endoskeletal elements were never part of
the dermal skeleton

Ex: scapula, vertebrae, ribs, sternum, brain case, and
extremity bones
Bone Evidence



All bone develops from mesenchyme
Neural crest cells
Membrane bone- arises from mesenchyme
without passing through cartilaginous
intermediate


exoskeleton
Replacement bone- arises from existing cartilage

endoskeleton
Endoskeletal Tissues

Visceral Skeleton

Jaw cartilages and ear ossicles



Weberian ossicles of fish (ear ossicles)
Derived from transverse processes of anterior most
vertebrae
Somatic Skeleton
Remaining internal bones developing from mesoderm
proper
 Somite and scleratome

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Axial Skeleton
Appendicular Skeleton
Vertebrae Development
Arise from sclerotome cells of somites
Morphogenesis

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Sclerotome divides into posterior and anterior halves
Halves join with segments of adjacent sclerotomes
Centrum formed from junction
Vertebrae are intersegmental
Myotome doesn’t move
Posterior segment forms costal process

Site of rib attachment
Vertebrae Development
Figure 9.1: (a) sclerotome divides (b) halves
join with adjacent halves of next sclerotome
(c) junction forms centrum.
Figure 9.2: Developing vertebral column
showing intersegmental position.
Axial Skeleton Vertebrae
Cartilaginous or bony
From occipital region to tail
Vertebrae types based on centrum structure


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Centrum is common feature in all vertebrae
Centrum Structure
Acelous- flat anterior and posterior surface

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Mammals
Amphicelous- concavities of anterior and posterior
surfaces

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Fish, primitive salamanders
Procelous- concanvity on anterior surface


Most reptiles
Opisthocelous- concavity of posterior surface


Most salamanders
Heterocelous- saddle-shaped


Neck of birds and turtles
Figure 9.3: Vertebral types based on articular surface of centra.
Vertebrae Evolution
Transition from crossopterygians
to labyrinthodonts
Different types of vertebrae
came from primitive,
rachitomous labyrinthodont
vertebrae


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
Two pleurocentra and U-shaped
hypocentrum
Hypocentrum is lost and
pleurocentrum enlarges and gives
rise to centrum of modern
amniote
Figure 9.4: Modifications from
labyrinthodont to modern amniote
vertebrae. Hypocentrum is diagonal
lines. Pleurocentrum is red.
Vertebrae Grouping
Grouped according to body region
Amphibians


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First to possess a cervical vertebrae
Figure 9.6: Regions
of vertebral column
Figure 9.5: Single
cervical vertebrae of
anuran.
Reptile Vertebrae


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Atlas as 1st and axis as
2nd cervicals
Turtle: 8 cervicals, 2
sacrals, 10 dorsals, 16-30
caudals
Alligator: 8 cervicals, 11
thoracic, 5 lumbar, 2
sacrals, up to 40 caudals
Figure 9.7: atlas and axis cervical vertebrae.
Figure 9.8: Dorsal view of sacral vertebrae of
vertebrates.
Bird Vertebrae


Possess atlas and axis
13-14 free cervicals, 4 fused thoracics,
fused synsacrum, free caudals, pygostyle
Figure 9.9: Pigeon vertebral column.

Synsacrum
Fuses with pelvic bone
 Reduction in bone mass

Figure 9.10: Pigeon skeleton: trunk, tail, and
pectoral girdle.
Figure 9.11: Synsacrum and pelvic
girdle left lateral (a) and ventral (b)
views.
Mammal Vertebrae
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most have 7 cervicals
12 thoracic and 5 lumbar compose dorsal
vertebrae
ancestral mammals possessed ~ 27 presacrals
sacrum 2-5 fused vertebrae (ankylosed)
caudals are variable

primates have 2-5 fused into coccyx
Ribs
Dogfish- develop dorsal ribs
Most teleost- develop ventral ribs
Tetrapods- have dorsal and ventral ribs
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Dorsal ribs lost, enlargement of head of
proximal ribs
2 portions articulate
with vertebrae

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Tuberculum- dorsal head
Capitulum- ventral head
Figure 9.12: Rib types - Dorsal and ventral
ribs.


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Agnathans- no ribs
Amphibians- ribs never
reach sternum
Birds- flat processes
extending off ribs
posteriorly (unicate
processes)
Figure 9.13: Unicate processes of bird.
Figure 9.14: Vertebrae and ribs of alligator.
Sternum



Tetrapod structure
Amphibians- poorly formed
Reptiles- cartilaginous plates

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Snakes, legless lizards, turtles have no sternum
Alligator- extends down belly


Ribs fused it sternum
Gastralia
Figure 9.15: Ribs and gastralia of alligator.

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Birds- unusual, keeled sternum in
carinates
Mammals- well developed sternum

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Rod shaped
Segments: manubrium, sternebrae,
xiphisternum and xiphoid process
Figure 9.16: Keeled sternum of bird.
Figure 9.17: Tetrapod sterna.
Heterotopic Bone



Develop by endochondral or intramembranous
ossification
In areas subject to continual stress
Ex: os cordis, rostral bone, os penis, os clitoridis

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Os cordis- interventricular septum
in deer heart
Rostral bone- snout of pig
Os penis (baculum)- embedded in
penis of lower primates
Os clitoridis- embedded in clitoris
of otters
Others include falciform,
sesamoid, patella, pisiform
Figure 9.18: Heterotopic bones
(book figure 7.11).
Skull and Visceral Skeleton

Two functionally independent cartilaginous
components derived from replacement bone
1. Neurocranium
2. Splanchnocranium
Figure 9.19: Placoderm skull; neurocranium
in blue; splanchnocranium in yellow.
Neurocranium


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Protects brain and anterior part of spinal cord
Sense organ capsules
Cartilaginous brain case is embryonic adaptation
Four ossification centers
Figure 9.20: Development of cartilaginous
neurocranium.
Neurocranium Ossification Centers

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Occiptial Region
Sphenoid Region
Ethmoid Region
Otic Region
Figure 9.21: Neurocranium of human skull.

Occipital Region
Basioccipital, 2 exoccipitals, suproccipital
 Forms single occipital bone in mammals


Sphenoid Region
Basisphenoid, orbitosphenoid,
presphenoid, laterosphenoid
 Fuse to form one sphenoid
bone in mammals

Figure 9.22: Sphenoid bone.
Figure 9.23: Human skull (a) cribriform
plate (b) crista galli (c) frontal bone (d)
sphenoid bone (e) temporal bone (f) sella
turcica.
Figure 9.24: Sphenoid bone.

Ethmoid Region
Anterior to sphenoid
 Cribriform plate, olfactory foramina, terminals,
mesamoid
 Fuse to form ethmoid in mammals
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Otic Region

Three bones in tetrapods
Prootic
 Opisthotic
 Epiotic

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Unite to form petrosal bone in birds and mammals

Forms temporal in mammals
Figure 9.25: Temporal bone of human skull.
Figure 9.26: Multiple nature of temporal
bone of mammals.
Figure 9.27: Intramembranous ossification of human
skull. Embryonic, cartilaginous neurocranium is
black. Neurocranial bones are red. Other is dermal
mesenchyme.
Splanchnocranium



Visceral skeleton
Visceral arches
Branchial region
Figure 9.28: Splanchnocranium of human.
Skeletal derivatives of 2nd through 5th
pharyngeal arches.

1st visceral arch- mandibular
Meckel’s cartilage  malleus
 Pteryoquadrate  incus


2nd visceral arch- hyoid
hyomandibula  columella (stapes)
 ceratohyal  styloid process and
anterior horn of hyoid
 basihyal  body of hyoid

Figure 9.29: Caudal end of Meckel’s
cartilage and developing middle ear
cavity.
Visceral-Cranial Derivatives
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Alisphenoid- part of sphenoid
Malleus, incus- 1st arch
Stapes- 2nd arch
Styloid- 2nd arch
Hyoid- mainly basihyal
Figure 9.30: Derivatives of the human
visceral skeleton (red).
Figure 9.31: Skeletal derivatives of pharyngeal arches.
Dermatocranium


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Membrane bone, not replacement bone
Dermal bones of skull
Upper jaw and face, palates, mandible
Figure 9.32: Pattern that tetrapod dermatocrania may have evolved.
Dermatocranium (cont.)
Figure 9.33: Dog skull showing dermatocranium
(pink), chondrocranium (blue), and
splanchnocranium (yellow).
Figure 9.34: Endochondral bones (red) of
mammalian skull.
Dermatocranial Elements
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Nasal
Squamosal
Secondary palate- premaxilla, maxilla, jugal
Primary palate- vomer, palatine, pterygoid
Neurocranial Elements
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Cribriform
Ethmoid
Otic complex
Temporal bone
Splanchnocranial Elements

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Maleus, incus, stapes
Styloid process- hyoid
Visceral Arches of Man
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Styloid processes
Body of hyoid
Thyroid
Cricoid
Middle Ear Bones
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Hammer (malleus_
Anvil (incus)
Stirrup (stapes)
Not homologous to weberian ossicles in teleost
fish

Modified transverse processes of anteriormost
vertebrae in some fishes.
Appendicular Skeleton


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Pectoral Girdle
Pelvic Girdle
Appendages
Adaptations for Speed
Pectoral Girdle

2 sets of elements: cartilage or
replacement bone and membrane
bone

Replacement bones


Coracoid, scapula, suprascapula
Membrane bones

Clavicle, cleithrum, supracleithrum
Figure 9.35: Pectoral girdle phylogenetic lines.
Dermal bones are red. Replacement bones are
black.
Reduction in number of
bones through evolution

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Shark- only cartilagenous
components
Alligator- retains only
replacement bone elements,
no dermal bone
Mammals


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Scapula of replacement bone
Clavicle of membrane bone
Birds- two clavicles fuse to
form furcula (wishbone)
(a)
(b)
Figure 9.36: Pectoral girdles of (a) Polypterus and (b)
shark.. Dermal bones are red. Replacement bones
are black..
Pelvic Girdle


No dermal elements
Three replacement bones


Ilium, ischium, pubis
Triradiate pelvic girdlealligator and dinosaur
Figure 9.37: Left halves of pelvic girdles showing
parallel evolution.
Appendages


Single unit in both fore and hind limbs most medial
Two units in fore and hind limb distal area
Figure 9.38: Dorsal view of left forelimb or forefin of Devonian tetrapods.
Figure 9.40: Left pectoral fin of Devonian fish
[left] and forelimb of early tetrapod [right].
Figure 9.39: Cladogram of lobe-Fin fishes
and amphibians.

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Small set of bones at wrist and ankle
Pentameristic pattern of phalanges
Reduction in number and position
of phalanges
Figure 9.41: Evolution of fins to limbs.
Adaptations for Speed

Plantigrade
Flat on the ground
 Primates

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Digitigrade
Elevated
 Carnivores
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Unguligrade
Reduction in digits
 Two types

Figure 9.42: Plantigrade, digitigrade, and unguligrade
feet. Ankle bones are black. Metatarsals are grey.
Unguligrade Adaptation
Reduction in digits

Perissodactyls

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Odd toed
Mesaxanic foot
Weight on enlarged middle
digit


Ex: horse
Artidodactyls

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Even toed
Paraxonic foot
Weight equally distributed on
3rd and 4th digits

Ex: camel
Figure 9.43: Unguligrade adaptations in
horse and camel. Bones lost are white.
Locomotion Without Limbs

Serpentine
Lateral undulation
 Wave motion
 Minimum 3 contact points


(a)
Rectilinear
Straight line
 Scutes on belly lift
 Costocutaneous muscles
move the skin

(b)
(c)
Figure 9.44: Serpentine locomotion (a) and rectilinear
locomotion (b & c).
Locomotion Without Limbs (cont.)

Sidewinding
Minimum 2 contact points
 Adaptation in sandy habitats


Concertina
Minimum 2 contact points
 Allows snake to move up
gutter

(a)
(b)
Figure 9.45: Sidewinding locomotion (a) and
concertina locomotion (b).
Literature Cited
Figure 9.1- http://www.brown.edu/Courses/BI0032/bone/axial2.htm
Figure 9.2, 9.3, 9.4, 9.5, 9.8, 9.9, 9.10, 9.11, 9.12, 9.14, 9.16, 9.17, 9.18, 9.20, 9.21, 9.25, 9.26, 9.27, 9.28, 9.29,
9.30, 9.31, 9.32, 9.34, 9.35, 9.36, 9.37, 9.40, 9.42 & 9.43- Kent, George C. and Robert K. Carr.
Comparative Anatomy of the Vertebrates. 9th ed. McGraw-Hill, 2001.
Figure 9.6- http://www.agrabilityproject.org/assistivetech/tips/tractorseat.cfm
Figure 9.7- http://www.spineuniverse.com/displayarticle.php/article2245.html
Figure 9.13- http://bioweb.uwlax.edu/zoolab/Table_of_Contents/Lab9b/Bird_Skeleton_1/Bird_Skeleton_1c/bird_skeleton_1c.htm
Figure 9.15- http://www.auburn.edu/academic/classes/zy/0301/Topic8/Topic8.html
Figure 9.19-Kardong, K. Vertebrates: Comparative Anatomy, Function, Evolution. McGraw Hill, 2002.
Figure 9.22- http://www.mlaphil.org/chronicle/20n3/fall2002.htm
Figure 9.23- http://www.staneksoftware.com/anatomy_bowl_content/SkSkull1.htm
Figure 9.24- http://www.upstate.edu/cdb/grossanat/hnsklatsb.shtml
Figure 9.33- Kardong, K. Vertebrates: Comparative Anatomy, Function, Evolution. McGraw Hill, 2002.
Figure 9.38- http://cas.bellarmine.edu/tietjen/images/subphylum_vertefish.htm
Figure 9.39- http://bss.sfsu.edu/holzman/courses/Fall%2003%20project/CAtigersalamander.htm
Figure 9.41- http://pharyngula.org/~pzmyers/MyersLab/teaching/Bi104/l02/fins.html
Figure 9.44- http://www.worldwidesnakes.com/ri-reptile-basic-anatomy-locomotion.php
Figure 9.45 (a)- http://folio.photosource.com/1120
Figure 9.45 (b)- http://voronoi.sbp.ri.cmu.edu/research/rsch_locomotion.html