15. Mouth, teeth, pharynx

The pharynx forms just posterior to that point. In Deuterostomes, mouth forms where the archenteron meets the stomodeum (a fold in ectoderm). The pharynx forms just posterior to that point. Early in ontogeny and phylogeny it has associated gill structures. Fig. 16.1 Liem, Bemis, Walker & Grande.

Pharynx performs respiratory and digestive system functions

The pharynx is the major respiratory structure in early vertebrates. Water high in O2 and low in CO2 enters pharynx via mouth and / or spiracle This water is forced across gills and out external gill slits Blood low in O2 and high in CO2 is pumped into gills where gas exchange takes place What mechanism makes gases move from water to blood or blood to water? Diffusion gradient

Walker and Homberger The pharynx is highly vascularized to allow it to function in respiration. Walker and Homberger

palate separates respiration from ingestion but systems cross paths 8= esophagus 13 = hard palate 33= trachea 28 = soft palate 21= vomero- nasal opening 24 = oral cavity 27 = nasal cavity palate separates respiration from ingestion but systems cross paths in the pharynx

Seven openings into pharynx 1 – oral cavity 2+3 – paired internal nares 4– esophagus 5– trachea 6+7 – paired eustachian tubes

a primary palate – primitive condition for Choanata a short secondary palate is present in Some turtles Crocodilians evolve A long secondary Palate, as in Alligator a primary palate – Still present in Dermochelys Synapsids evolve A long secondary Palate, as in Homo and Canis Surrounds Internal nares a primary palate – primitive condition for Choanata

A. Longitudinal section – cartilages only Fig. 10-20 Walker and Homberger – The larynx of the cat A. Longitudinal section – cartilages only B. Lateral view of the laryngeal and tracheal cartilages C. Lateral view of the laryngeal muscles with hyoid added

Walker and Homberger Muscles of the pharyngeal region Fig. 7-20

(thyroid cartilage) Walker and Homberger

Tongue – modified hypobranchial muscle anchored by hyoid apparatus Tongue function: 1- food handling 2- taste buds 3- move scent to vomeronasal organ 4- prey capture Mastoid process 5- grooming 6- speech Lingual or glossal refers to tongue Genio refers to chin = Adam’s apple Marieb

Function of epiglottis Superior esophageal sphincter Superior esophageal sphincter Function of epiglottis Marieb

Basic Terms Used for Feeding Mechanisms of Vertebrates 1. Suspension-feeding (= filter-feeding) - filter small particles (alive or dead, depending on species) out of water column 2. Suction-feeding - open mouth, suck in food 3. Ram-feeding - open mouth, swim over food Ram-Suction Index - compares movement of food relative to movement of feeder 4. Inertial-feeding - inertia of food is used to move it in oral cavity 5. Transport - movement of food within oral cavity (by water currents in aquatic vertebrates or tongue in tetrapods) 6. Mastication - physical reduction of food size by chewing Liem, Bemis, Walker & Grande.

Mastication requires teeth Primitively homodont, and non-occlusal With a variety of tooth attachment types and tooth replacement modes

Some Important Terms for Teeth Polyphyodont - multiple generations of tooth replacement (most vertebrates) Diphyodont - two sets of teeth: milk and permanent (most mammals; incisor, canine and premolar teeth are replaced) Monophyodont - a single set of teeth (e.g., cetaceans) Homodont - teeth of similar shape along jaw Heterodont - teeth of different shape along the jaw Tooth plate or Toothplate - at least two uses are common: 1. Many individual teeth fused together at their bases; separate cusps are still visible (e.g., in pharynx of fishes) 2. Fusion of individual teeth during ontogeny: separate cusps may not still be visible (e.g., lungfishes, chimaeras) Liem, Bemis, Walker & Grande.

Types of Mammalian Teeth and Dental Formulae Heterodonty has produced four tooth types: Types of Mammalian Teeth and Dental Formulae Incisor teeth (I), typically these are replaced Canine teeth (C), typically these are replaced Premolar teeth (P), typically these are replaced Molar teeth (M), typically these are not replaced Formulae are expressed as type # in upper jaw/# in lower jaw I 5/4, C 1/1, P 2/2, M 4/4 = opossum I 2/2, C 1/1, P 2/2, M 3/3 = humans Liem, Bemis, Walker & Grande.

Carnassial Pair: P4-M1 “Montre moi vos dents, et je vous dit que vous est” Carnassial Pair: P4-M1 Fig. 16.6 Liem, Bemis, Walker & Grande.