1. Comparative Anatomy Bone
Kardong
Chapters 7, 8, & 9
Part 9

2. Organization of Skeletal Tissues
Figure 9.1.

3. Bone Legacy Exoskeleton or dermal skeleton
Dermal bony armor of ostracoderms
Bony scales in ancient fish
Cranial dermal armor arose from neural crest cells

4. Other endoskeletal elements were never part of the dermal skeleton
Endoskeleton
Internal to skin
Were once exoskeleton
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

5. 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

6. Endoskeletal Tissues Visceral Skeleton Somatic Skeleton Axial Skeleton
Jaw cartilages and middle ear bones
Weberian ossicles of fish (are referred to as ear ossicles)
Derived from transverse processes of anterior most vertebrae
Somatic Skeleton
Remaining internal bones developing from mesoderm proper
Sclerotome of somite
Axial Skeleton
Appendicular Skeleton

7. Vertebrae Development
Arise from sclerotome cells of somites
Morphogenesis
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

8. Vertebrae Development (cont’d.)
Figure (a) sclerotome divides (b) halves join with adjacent halves of next sclerotome (c) junction forms centrum (see book figure 8.12)
Figure Developing vertebral column showing intersegmental position
(see book figure 8.12).

9. Axial Skeleton Vertebrae
Cartilaginous or bony
From occipital region to tail
Vertebrae types based on centrum structure
Centrum is common feature in all vertebrae

10. Centrum Structure Acelous- flat anterior and posterior surface
Mammals
Amphicelous- concavities of anterior and posterior surfaces
Fish, primitive salamanders
Procelous- concavity on anterior surface
Most reptiles
Opisthocelous- concavity of posterior surface
Most salamanders
Heterocelous- saddle-shaped
Neck of birds and turtles

11. Figure 9.4. Vertebral types based on articular surface of centra (book figure 8.4).

12. Vertebrae Evolution
Transition from crossopterygians to labyrinthodonts
Different types of vertebrae came from primitive, rachitomous labyrinthodont vertebrae
Two pleurocentra and U-shaped hypocentrum
Hypocentrum is lost and pleurocentrem enlarges and gives rise to centrum of modern amniote
Figure Modifications from labyrinthodont to modern amniote vertebrae. Hypocentrum is diagonal lines. Pleurocentrum is red
(see book figure 8.3).

13. Vertebrae Grouping Grouped according to body region Amphibians
First to possess a cervical vertebrae
Figure Regions of vertebral column.
Figure Single cervical vertebrae of anuran (book figure 8.13).

14. Reptile Vertebrae Atlas as 1st and axis as 2nd cervicals
Turtle: 8 cervicals, 2 sacrals, 10 dorsals, caudals
Alligator: 8 cervicals, 11 thoracic, 5 lumbar, 2 sacrals, up to 40 caudals
Figure atlas and axis cervical vertebrae.
Figure Dorsal view of sacral vertebrae of vertebrates.

15. Bird Vertebrae Possess atlas and axis
13-14 free cervicals, 4 fused thoracics, fused synsacrum, free caudals, pygostyle
Figure Pigeon vertebral column (see book figure 8.31).

16. Synsacrum Fuses with pelvic bone Reduction in bone mass
Figure Synsacrum and pelvic girdle left lateral (a) and ventral (b) views (book figure 8.31).
Figure Pigeon skeleton: trunk, tail, and pectoral girdle.

17. Mammal Vertebrae Most species 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

18. Ribs Dogfish- develop dorsal ribs Most teleost- develop ventral ribs
Tetrapods- have dorsal and ventral ribs
Current theory is that the tetrapod rib is homologous to the dorsal rib of fishes
Primitive tetrapods have bicipital ribs - 2 portions articulate with vertebrae
Tuberculum- dorsal head
Capitulum- ventral head
Figure Dorsal and ventral ribs
(book figure 8.6 and 8.7).

19. Figure 9.14. Uncinate processes of bird (see book
Agnathans- no ribs
Amphibians- ribs never reach sternum
Birds- flat processes extending off ribs posteriorly (uncinate processes)
Figure Uncinate processes of bird (see book
figure 8.8).
Figure Vertebrae and ribs of alligator (book figure 8.2).

20. Sternum Strictly a tetrapod structure Amphibians- poorly formed
Reptiles - cartilaginous plates
Snakes, legless lizards, turtles have no sternum
Alligator- extends down belly
Ribs fused it sternum
Gastralia
Figure Ribs and gastralia of alligator (book figure
8.2).

21. Figure 9.18. Tetrapod sterna
Birds- unusual, keeled sternum in carinates
Mammals- well developed sternum
Rod shaped
Segments: manubrium, sternebrae, xiphisternum and xiphoid process
Figure Tetrapod sterna
(book figure 8.8).
Figure Keeled sternum of bird
(book figure 8.8).

22. Heterotopic Bone
Develop by endochondral or intramembranous ossification
In areas subject to continual stress
Ex: Os cordis, rostral bone, os penis, os clitoridis

23. 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 Heterotopic bones.

24. Skull and Visceral Skeleton
Two functionally independent cartilaginous components derived from replacement bone
1. Neurocranium
(= chondrocranium)
2. Splanchnocranium
Figure Dog skull. Sources of
the various bones are outlined:
dermatocranium (pink),
neurocranium (= chondrocranium)-
(blue); splanchnocranium (yellow)

25. Neural Crest Contributions to the Skull
Figure 9.21.

26. Neurocranium Protects brain and anterior part of spinal cord
Sense organ capsules
Cartilaginous brain case is embryonic adaptation
Four ossification centers
Figure Development of cartilaginous neurocranium (book figure 7.3).

27. Neurocranium Ossification Centers
Occipital region
Sphenoid region
Ethmoid region
Otic region
Figure Neurocranium of human skull.

28. Occipital Region Sphenoid Region
Basioccipital, 2 exoccipitals, supraoccipital
Forms single occipital bone in mammals
Sphenoid Region
Basisphenoid, orbitosphenoid, presphenoid, laterosphenoid
Fuse to form one sphenoid
bone in mammals
Figure Sphenoid bone.

29. Figure Sphenoid bone.
Figure Human skull (a) cribriform plate (b) frontal bone (c) temporal bone (d) ethmoid bone (e) sphenoid bone (f) foramen magnum.

30. Ethmoid Region Otic Region Anterior to sphenoid
Cribriform plate, olfactory foramina, terminals, mesamoid
Fuse to form ethmoid in mammals
Otic Region
Three bones in tetrapods
Prootic
Opisthotic
Epiotic
Unite to form petrosal bone in birds and mammals
Forms temporal in mammals

31. Figure 9.27. Temporal bone of human skull (book figure 9.28).
Figure Multiple nature of temporal bone of mammals (see book figure 7.53).

32. Figure 9. 29. Intramembranous ossification of human skull
Figure Intramembranous ossification of human skull. Embryonic, cartilaginous neurocranium is black. Neurocranial bones are red. Other is dermal mesenchyme.

33. Splanchnocranium Viscerocranium, although a misnomer.
- Visceral arches
- Branchial region
Figure Splanchnocranium of human. Skeletal derivatives of 2nd through 5th pharyngeal arches (see book Table 7.2).
Figure Primitive splanchnocranium.

34. 1st visceral arch- mandibular Meckel’s cartilage  malleus
Palatoquadrate (quadrate)  incus
2nd visceral arch- hyoid
hyomandibula  columella (stapes)
ceratohyal  styloid process and anterior horn of hyoid
basihyal  body of hyoid
Figure Caudal end of Meckel’s cartilage and developing middle ear cavity.

35. Viscerocranial Derivatives
Alisphenoid- part of sphenoid
Malleus, incus- 1st arch
Stapes- 2nd arch
Styloid- 2nd arch
Hyoid- mainly basihyal
Figure Derivatives of the human visceral skeleton (red).

36. Figure 9. 34. Skeletal derivatives of pharyngeal arches (book Table 7

37. Dermatocranium Membrane bone, not replacement bone
Dermal bones of skull
Upper jaw and face, palates, mandible
Figure Pattern that tetrapod dermatocrania (see book figure 7.10).

38. Dermatocranium (con’t.)
Figure Dog skull showing dermatocranium (pink), chondrocranium (blue), and splanchnocranium (yellow).
Figure Hypothetical derivations of skull bones. (Box Essay 7.1)

39. Dermatocranial Elements
Nasal, frontal, parietal, squamosal (facial and roofing bones)
Dentary
Vomer, palatine, pterygoid (primary palate)
Premaxilla, maxillary, jugal (secondary palate)
Figure Lizard skull.

40. Evolution of Mammalian Middle Ear Bones
Figure (book figure 7.55).

41. Phylogeny of the
Splanchnocranium
Figure (book figure 7.66).

42. Appendicular Skeleton
Pectoral Girdle
Pelvic Girdle
Appendages
Adaptations for Speed

43. Pectoral Girdle
2 sets of elements: cartilage or replacement bone/membrane bone
Replacement bones
Coracoid, scapula, suprascapula
Membrane bones
Clavicle, cleithrum, supracleithrum
Figure Pectoral girdle along phylogenetic lines.
Dermal bones are red. Replacement bones are black.

44. Reduction in number of bones through evolution
Shark- only cartilagenous components
Alligator- retains only replacement bone elements, no dermal bone
Mammals
Scapula of replacement bone
Clavicle of membrane bone
Birds- two clavicles form furcula (wishbone)
(a)
(b)
Figure Pectoral girdles of (a) Polypterus and (b) shark.. Dermal bones are red. Replacement bones are black.

45. Fish – Tetrapod Transition
Figure (book figure 9.16).

46. Summary of Pectoral
Girdle Evolution
Figure (book figure 9.19).

47. Pelvic Girdle No dermal elements Three replacement bones
Ilium, ischium, pubis
Triradiate pelvic girdle- alligator and dinosaur
Figure Left halves of pelvic girdles showing
parallel evolution.

48. Summary of Pelvic Girdle Evolution
Figure (book
figure 9.21).

49. Appendages Single unit most medial in both fore and hind limbs
Two units in distal region of fore and hind limb
Figure Dorsal view of left forelimb or forefin of Devonian tetrapods.

50. Figure 9.48. Cladogram of lobe-Fin fishes
and amphibians.
Figure Basic organization of fore- and
hindlimb (book figure 9.23).

51. Small set of bones at wrist and ankle
Pentameristic pattern of phalanges
Reduction in number and position of phalanges
Figure Evolution of fins to limbs.

52. Figure Adaptations in
secondarily aquatic tetrapods.
(book figure 9.30)

53. Adaptations for Speed Plantigrade Digitigrade Unguligrade
Flat on the ground
Primates
Digitigrade
Elevated
Carnivores
Unguligrade
Reduction in digits
Two types
Figure Plantigrade, digitigrade, and unguligrade feet. Ankle bones are black. Metatarsals are gray.

54. Unguligrade Adaptations Reduction in digits
Perissodactyl
Odd toed
Mesaxanic foot
- Weight on enlarged middle digit
Ex: horse
Artidodactyl
Even toed
Paraxonic foot
- Weight equally distributed on 3rd and 4th digits
Ex: camel
Figure Unguligrade adaptations in horse and camel. Bones lost are white (see book figure 9.39).

55. Skeletal Adaptations for Digging
Figure (book figure 9.58).

56. Locomotion Without Limbs
Serpentine
Lateral undulation
Wave motion
Minimum 3 contact points
Rectilinear
Straight line
Scutes on belly lift
Costocutaneous muscles move the skin
(a)
(b)
(c)
Figure Serpentine locomotion (a) and rectilinear locomotion (b & c)

57. Locomotion Without Limbs (cont’d.)
Sidewinding
Minimum 2 contact points
Adaptation in sandy habitats
Concertina
Allows snake to move up
gutter
(a)
(b)
Figure Sidewinding locomotion (a) and concertina locomotion (b)

58. Brachiation: Human Limb Engineering
Figure (book page 354).
Five to 10 million years have passed
since distant human ancestors swung
through trees (Kardong, 2013).