lec1 anatomy

• Comparative Anatomy


  A branch of science that deals with the structure of animals, and with the similarities, as well as differences in this structure
• Comparative Anatomy focuses on the comparative study of vertebrates and a few of their closest relatives, all of which are included in the phylum chordate
• Vertebrates and their closest relatives

  • Coelomate, metameric and bilaterally symmetrical animals (in the muscular, skeletal and nervous system)
  • Cephalization or head formation (combination of several anterior segment containing brain and sense organs)
  • Brain is a complicated (fore-, mid- and hind-brain), Paired cranial nerves (10-12), Paired sensory organs (except olfactory of Petromyzon)
• Vertebrates


  • Possession of the skull or cranium which protects the brain and sense organs, Cartilage in all the embryos (chondrocranium), changed to a bony skull (osteocranium) in the adult
  • Possess a notochord, embryonic condition, replaced by the vertebral column in the adult
  • The epidermis becomes a stratified epithelium, Mucous glands in aquatic forms, Cornified in terresterial forms
  • The pharynx is provided with gill slits, embryonic condition, continue in aquatic forms and replaced by lungs, The mouth contains a tongue and usually teeth
  • The circulatory system is closed and a heart of three chambers at least, The blood contains red and white blood corpuscles, Haemoglobin pigment is present
  • Presence of true coelom, divided into pericardial cavity and perivisceral cavity
  • Presence of two kidneys with two ureters
  • Presence one pair of gonads (except Petromyzon) provided with genital ducts carrying their products
• The comparative anatomist recognizes that the vertebrates and some of their close relatives are built upon the same fundamental plan and that there is often a close correspondence even in detail
• Within the general vertebrate plan there may be many variations which are, for the most part, adaptive in nature
• Homologous organs


  Similar in origin or developmental history and usually similar in structure
• Homologous organs


  • The skeleton of the forelimb of a cat, the arm of man, the flipper of the whale, the wing of the bat and the wings of birds
• Analogous organs


  Similar in use or function but not necessary of origin
• Analogous organs


  • The wings of birds and butterflies
• Ontogeny


  The events taking place during the development of an organism
• Phylogeny


  Concerns with the history of the race or group
• Biogenetic Law


  Recapitulation theory (by Haeckel), which states that during development an individual passes through certain ancestral stages through which the entire race passed in its evolution, and that the embryos of higher forms in certain ways resemble the adults of lower forms
• The Biogenetic Law was used to explain why structures like pharyngeal pouches and aortic arches should make their appearance in the embryos of higher vertebrates
• Anterior


  The part that moves forward (the head)
• Posterior


  The opposite end of the anterior
• Dorsal


  The upper or back surface
• Ventral


  The lower or belly surface
• Medial


  A position near to the mid-line
• Lateral


  A more removed position from the mid-line
• Proximal


  The part of a structure closer to the center of the body or some important point of reference
• Distal


  The part of a structure farther removed from the center of the body or some important point of reference
• The Echinoderm theory appears to be the most reasonable one for the ancestry of chordates
• Echinoderms are radially symmetrical animals and show no typical chordate characters yet they seem to be most closely related to chordates
• The Sea cucumber larva, called auricularia is a free-swimming, bilaterally symmetrical larva, and it very closely resembles the larva of the hemichordates which is known as tornaria
• A series of changes may have taken place in the auricularia larva by which it changed into an ancestral chordate
• The comparative study of vertebrates and their closest relatives is classified under the phylum Chordata