Comparative Anatomy Bone Kardong Chapters 7, 8, & 9 Part 9
Organization of Skeletal Tissues Figure 9.1.
Bone Legacy Exoskeleton or dermal skeleton Dermal bony armor of ostracoderms Bony scales in ancient fish Cranial dermal armor arose from neural crest cells
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
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 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
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
Vertebrae Development (cont’d.) Figure 9.2. (a) sclerotome divides (b) halves join with adjacent halves of next sclerotome (c) junction forms centrum (see book figure 8.12) Figure 9.3. Developing vertebral column showing intersegmental position (see book figure 8.12).
Axial Skeleton Vertebrae Cartilaginous or bony From occipital region to tail Vertebrae types based on centrum structure Centrum is common feature in all vertebrae
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
Figure 9.4. Vertebral types based on articular surface of centra (book figure 8.4).
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 9.5. Modifications from labyrinthodont to modern amniote vertebrae. Hypocentrum is diagonal lines. Pleurocentrum is red (see book figure 8.3).
Vertebrae Grouping Grouped according to body region Amphibians First to possess a cervical vertebrae Figure 9.7. Regions of vertebral column. Figure 9.6. Single cervical vertebrae of anuran (book figure 8.13).
Reptile Vertebrae 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 9.8. atlas and axis cervical vertebrae. Figure 9.9. 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 9.10. Pigeon vertebral column (see book figure 8.31).
Synsacrum Fuses with pelvic bone Reduction in bone mass Figure 9.12. Synsacrum and pelvic girdle left lateral (a) and ventral (b) views (book figure 8.31). Figure 9.11. Pigeon skeleton: trunk, tail, and pectoral girdle.
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
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 9.13. Dorsal and ventral ribs (book figure 8.6 and 8.7).
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 9.14. Uncinate processes of bird (see book figure 8.8). Figure 9.15. Vertebrae and ribs of alligator (book figure 8.2).
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 9.16. Ribs and gastralia of alligator (book figure 8.2).
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 9.18. Tetrapod sterna (book figure 8.8). Figure 9.17. Keeled sternum of bird (book figure 8.8).
Heterotopic Bone Develop by endochondral or intramembranous ossification In areas subject to continual stress Ex: Os cordis, rostral bone, os penis, os clitoridis
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 9.19. Heterotopic bones.
Skull and Visceral Skeleton Two functionally independent cartilaginous components derived from replacement bone 1. Neurocranium (= chondrocranium) 2. Splanchnocranium Figure 9.20. Dog skull. Sources of the various bones are outlined: dermatocranium (pink), neurocranium (= chondrocranium)- (blue); splanchnocranium (yellow)
Neural Crest Contributions to the Skull Figure 9.21.
Neurocranium Protects brain and anterior part of spinal cord Sense organ capsules Cartilaginous brain case is embryonic adaptation Four ossification centers Figure 9.22. Development of cartilaginous neurocranium (book figure 7.3).
Neurocranium Ossification Centers Occipital region Sphenoid region Ethmoid region Otic region Figure 9.23. Neurocranium of human skull.
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 9.24. Sphenoid bone.
Figure 9.26. Sphenoid bone. Figure 9.25. Human skull (a) cribriform plate (b) frontal bone (c) temporal bone (d) ethmoid bone (e) sphenoid bone (f) foramen magnum.
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
Figure 9.27. Temporal bone of human skull (book figure 9.28). Figure 9.28. Multiple nature of temporal bone of mammals (see book figure 7.53).
Figure 9. 29. Intramembranous ossification of human skull Figure 9.29. Intramembranous ossification of human skull. Embryonic, cartilaginous neurocranium is black. Neurocranial bones are red. Other is dermal mesenchyme.
Splanchnocranium Viscerocranium, although a misnomer. - Visceral arches - Branchial region Figure 9.31. Splanchnocranium of human. Skeletal derivatives of 2nd through 5th pharyngeal arches (see book Table 7.2). Figure 9.30. Primitive splanchnocranium.
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 9.32. Caudal end of Meckel’s cartilage and developing middle ear cavity.
Viscerocranial Derivatives Alisphenoid- part of sphenoid Malleus, incus- 1st arch Stapes- 2nd arch Styloid- 2nd arch Hyoid- mainly basihyal Figure 9.33. Derivatives of the human visceral skeleton (red).
Figure 9. 34. Skeletal derivatives of pharyngeal arches (book Table 7
Dermatocranium Membrane bone, not replacement bone Dermal bones of skull Upper jaw and face, palates, mandible Figure 9.35. Pattern that tetrapod dermatocrania (see book figure 7.10).
Dermatocranium (con’t.) Figure 9.36. Dog skull showing dermatocranium (pink), chondrocranium (blue), and splanchnocranium (yellow). Figure 9.37. Hypothetical derivations of skull bones. (Box Essay 7.1)
Dermatocranial Elements Nasal, frontal, parietal, squamosal (facial and roofing bones) Dentary Vomer, palatine, pterygoid (primary palate) Premaxilla, maxillary, jugal (secondary palate) Figure 9.38. Lizard skull.
Evolution of Mammalian Middle Ear Bones Figure 9.39. (book figure 7.55).
Phylogeny of the Splanchnocranium Figure 9.40. (book figure 7.66).
Appendicular Skeleton Pectoral Girdle Pelvic Girdle Appendages Adaptations for Speed
Pectoral Girdle 2 sets of elements: cartilage or replacement bone/membrane bone Replacement bones Coracoid, scapula, suprascapula Membrane bones Clavicle, cleithrum, supracleithrum Figure 9.41. Pectoral girdle along phylogenetic lines. Dermal bones are red. Replacement bones are black.
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 9.42. Pectoral girdles of (a) Polypterus and (b) shark.. Dermal bones are red. Replacement bones are black.
Fish – Tetrapod Transition Figure 9.43. (book figure 9.16).
Summary of Pectoral Girdle Evolution Figure 9.44. (book figure 9.19).
Pelvic Girdle No dermal elements Three replacement bones Ilium, ischium, pubis Triradiate pelvic girdle- alligator and dinosaur Figure 9.45. Left halves of pelvic girdles showing parallel evolution.
Summary of Pelvic Girdle Evolution Figure 9.46. (book figure 9.21).
Appendages Single unit most medial in both fore and hind limbs Two units in distal region of fore and hind limb Figure 9.47. Dorsal view of left forelimb or forefin of Devonian tetrapods.
Figure 9.48. Cladogram of lobe-Fin fishes and amphibians. Figure 9.49. Basic organization of fore- and hindlimb (book figure 9.23).
Small set of bones at wrist and ankle Pentameristic pattern of phalanges Reduction in number and position of phalanges Figure 9.50. Evolution of fins to limbs.
Figure 9.51. Adaptations in secondarily aquatic tetrapods. (book figure 9.30)
Adaptations for Speed Plantigrade Digitigrade Unguligrade Flat on the ground Primates Digitigrade Elevated Carnivores Unguligrade Reduction in digits Two types Figure 9.52. Plantigrade, digitigrade, and unguligrade feet. Ankle bones are black. Metatarsals are gray.
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 9.53. Unguligrade adaptations in horse and camel. Bones lost are white (see book figure 9.39).
Skeletal Adaptations for Digging Figure 9.54. (book figure 9.58).
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 9.55. Serpentine locomotion (a) and rectilinear locomotion (b & c)
Locomotion Without Limbs (cont’d.) Sidewinding Minimum 2 contact points Adaptation in sandy habitats Concertina Allows snake to move up gutter (a) (b) Figure 9.56. Sidewinding locomotion (a) and concertina locomotion (b)
Brachiation: Human Limb Engineering Figure 9.57. (book page 354). Five to 10 million years have passed since distant human ancestors swung through trees (Kardong, 2013).