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Hypaxial refers to ventral muscles and related structures while epaxial refers to more dorsal muscles. The horizontal septum divides these two regions in vertebrates from cyclostomes to gnathostomes. In terrestrial chordates , the myomeres become fused as well as indistinct, due to the disappearance of myosepta.
In fish a countercurrent flow (lower diagram) of blood and water in the gills is used to extract oxygen from the environment. [6] [7] [8] All basal vertebrates breathe with gills. The gills are carried right behind the head, bordering the posterior margins of a series of openings from the esophagus to the exterior.
Most of these frogs are caught in the wild, but some are raised in captivity. The United States is a net importer of frog legs. [68] The American bullfrog is used as a specimen for dissection in many biology and anatomy classes in schools across the world. [69] It is the state amphibian of Missouri, Ohio, and Oklahoma. [70]
Along with frogs and earthworms, fetal pigs are among the most common animals used in classroom dissection. There are several reasons for this, including that pigs, like humans, are mammals. Shared traits include common hair, mammary glands, live birth, similar organ systems, metabolic levels, and basic body form.
A dissected spotted African lungfish showing the notochord The notochord is the defining feature ( synapomorphy ) of chordates , and was present throughout life in many of the earliest chordates. Although the stomochord of hemichordates was once thought to be homologous or from a common lineal origin, it is now viewed as analogous, convergent ...
Dissection of a frog. Pain is an aversive sensation and feeling associated with actual, or potential, tissue damage. [1] It is widely accepted by a broad spectrum of scientists and philosophers that non-human animals can perceive pain, including pain in amphibians.
This research included the muscular response to opiates and static electricity, for which experiments the spinal cord and rear legs of a frog were dissected out together and the skin removed. In 1781, [5] an observation was made while a frog was being dissected.