skeleton - 10/4/2011 Skeletal System Importance to the...

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10/4/2011 1 Skeletal System Importance to the study of comparative anatomy Bone is readily fossilized The skeleton is generally conservative Responds to important environmental and habitat changes Connective Tissue – “Living cells embedded (surrounded, suspended) in a non- living matrix (ground substance).” Includes: bone, cartilage, tendons, ligaments, blood All arise from a special mesodermal tissue called mesenchyme Cartilage Living cells ( chondrocytes ) isolated in pockets ( lacunae ) and surrounded by a non-living ground substance ( chondromucoprotein ). Covered by dense regular connective tissue perichondrium . Formed by chondrogenesis from inner layer of perichondrium. Two basic types: 1. hyaline cartilage precursor of replacement bone, also found on articular surfaces. 2. fibrous cartilages includes: 1. fibrocartilage 2. elastic cartilage 3. calcified cartilage Bone Living cells ( Osteocytes ) isolated in pockets ( lacunae ) and surrounded by a non-living ground substance ( hydroxyapatite ). Covered by dense regular connective tissue periosteum . Osteocytes intercommunicate via tiny canaliculi Haversian Systems provide bone with a generous supply of blood vessels and nerves.
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10/4/2011 2 Skeletal System Classification of Bone - by type of ossification 1. DERMAL BONE (Membrane Bone) Forms in the dermis Undergoes direct ossification, is not preformed in cartilage. Grows by accretion only. 2. ENDOCHONDRAL BONE (Replacement Bone) Formed by endochondral ossification , is performed in hyaline cartilage. Endochondral Ossification Structure formed first as cartilage. Diaphysis - primary center of ossification Epiphyses - secondary centers of ossification . Initially are separated from the diaphysis by growth zones ( zone of proliferating cartilage ) THE VERTEBRATE SKELETON Dermal Skeleton - Vertebrate Exoskeleton Forms the bone of dermal scales prominent in ancient fishes, boney fishes restricted in tetrapods, to skull, jaw and pectoral girdle elements Endoskeleton - Deep (internal) structures - 3 divisions 1. Somatic Skeleton Axial Skeleton - notochord, braincase, vertebral column, ribs, and sternum Appendicular Skeleton - paired appendages, pectoral and pelvic girdles 2. Visceral Skeleton - skeletal elements of the gills and structures evolutionarily derived therefrom. e.g. some elements of upper and lower jaws, middle ear bones of higher vertebrates 3. Heterotopic Bones - miscellaneous bones, formed by direct ossification Sesamoid Bones - form along tendons, e.g. patella interventricular bone in heart of certain ungulates (os cordis of deer) eyelid bones - crocodiles epipubic bones of proto and metatherians os penis (baculum), os clitoris (balbella) of mammals - heterotopic bones that support the external genetalia of some mammals
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10/4/2011 3 AXIAL SKELETON Centra (pleurocentra):
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skeleton - 10/4/2011 Skeletal System Importance to the...

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