It lies in the branchial region of the trunk.Externally its wall bears a longitudinal constriction along each lateral side. These lateral constrriction project into its lumen as ridges,called parabranchial ridges,consisting of tall columnar cells.These ridges incompletely divide the pharynx into a dorsal respiratory or branchial portion and a ventral digestive portion.The dorsal branchial portion is perforated dorso-laterally by two rows of U-shaped gill-slits ,and is concerned with respiration.The ventral digestive portion,lined with ciliated epithelium with gland cells,helps in food concentration.
No comments:
Post a Comment