Animal morphology lecture

• Major Subdivisions of the Digestive System

  • Buccal cavity
  • Pharynx
  • Esophagus
  • Stomach
  • Small and large intestines
  • Cloaca (anus)
• Accessory Organs of the Digestive System

  • Tongue
  • Teeth
  • Oral glands
  • Pancreas
  • Liver
  • Gall bladder
• Differences in anatomy of vertebrates

  • Nature and abundance of food
  • Readily absorbed
  • Extensive enzymatic activity
  • Constant food supply
  • Scattered supply
• Development of the gut

  1. Embryo lengthens

  2. Endoderm drawn out into tube

  3. Tube is more or less straight - outgrowth (diverticula)

  4. Posterior to stomach

  5. Liver, gall bladder, pancreas, and various ducts of organs; allantois

  6. Muscular and connective tissue associated with gut- mesodermal origin
• Embryonic Digestive Tract of Vertebrates

  • Midgut
  • Yolk
  • Attached yolk sac
  • Foregut
  • Oral cavity
  • Pharynx
  • Esophagus
  • Stomach
  • Small intestine
  • Hindgut
  • Large intestine
  • Cloaca
• Parts of the Mouth and Oral Cavity

  • Tongue
  • Teeth
  • Palate
• Palate


  Roof of oral cavity
• Bones of the Palate

  • Vomer
  • Pterygoids
  • Parasphenoid (medial)
  • Palatines
  • Ectopterygoids (lateral)
• Primary Palate


  Internal nares (choanae) lead to oral cavity anteriorly
• Secondary Palate


  • Nasal passages located above and open at end of oral cavity
  • Forms from palatal folds of lateral bones
  • Hard (anterior) and soft (posterior) palate
• Types of Teeth


  • Thecodont
  • Acrodont
  • Pleurodont
• Thecodont


  Sunk into sockets, found in reptiles and mammals
• Acrodont


  Shallow sockets attached to crest of bones, found in snakes
• Pleurodont


  Attached medial side of bone, found in lizards
• Specialized Teeth in Mammals

  • Incisors
  • Canines
  • Premolars
  • Molars
• Incisors

  Cutting teeth
• Canines


  Piercing and biting teeth
• Premolars and Molars


  Teeth for macerating food
• Dental Formula


  Expression of the number of each kind of tooth on side of head
• Tooth Crown Types


  • Brachyodont
  • Hypsodont
  • Bunodont
  • Lophodont
  • Selenodont
• Brachyodont


  Crowns are low, found in humans and pigs
• Hypsodont

  Crowns are high, found in horses and herbivores
• Bunodont

  Rounded peaks, found in omnivores
• Lophodont

  Cusps straight, found in perissodactyls and rodents
• Selenodont


  Crescent shape, found in artiodactyls
• Functions of the Vertebrate Tongue

  • Capturing and gathering food
  • Taste
  • Manipulating fluids and solids in oral cavity
  • Swallowing
  • Thermoregulation
  • Grooming
  • Human speech
• Tongue Mobility in Different Vertebrates

  • Cyclostome
  • Fishes
  • Tetrapod
  • Snakes, insectivorous lizards, amphibians and some birds
  • Mammals
• Cyclostome Tongue

  Derived from floor of pharynx
• Fishes Tongue


  Lack tongue
• Tetrapod Tongue

  • Hypobranchial muscle supported by hyoid
  • Bear taste buds
  • Vomeronasal organ (jacobson organs)
  • Lingual feeding (intraoral transport)
• Snakes, insectivorous lizards, amphibians and some birds Tongue

  • Largely immobilized in floor of oral cavity and cannot be extended
  • Sometimes long
  • Move in and out of oral cavity
• Mammal Tongue

  • Attached to floor of oral cavity (via frenulum)
  • Can still extend out of oral cavity
• Functions of Oral Glands


  • Secrete saliva
  • Secrete poison (lizards, snakes, and mammals)
  • Secrete anticoagulant (vampire bats)
• Saliva


  • Lubricates and binds food
  • Contains lysozyme to prevent overgrowth of oral microbes
  • Solubilizes dry food so it can be tasted
• Parts of the Pharynx

  • Glottis (slit leading to larynx)
  • Auditory openings (eustachian tube)
  • Esophagus opening
  • Epiglottis anterior to esophagus near trachea
• Mammal Pharynx


  • Epiglottis positioned over the glottis
  • When mammal swallows, larynx is drawn forward against epiglottis to block glottis and prevent food/liquid entering trachea
• Larynx Structures


  • Hyoid bone
  • Cricoid cartilage
  • Corniculate cartilage
  • Arytenoid cartilage
  • Thyroid facet
  • Thyroid cartilage
  • Cricoid cartilage
• Layers of the Gut Wall

  • Mucosa
  • Submucosa
  • Muscularis externa
  • Serosa
• Mucosa


  Innermost layer with 3 parts: epithelium, lamina propria, and muscularis mucosae
• Submucosa


  Stratum of loose connective tissue with nerves, capillaries, and lymphatic ducts