THE VERTEBRATE BODY PLAN

• Developmentally, the human (mammalian - vertebrate) body consists of a tube within a tube body plan. The inner tube gives rise to visceral structures. The outer tube (= body wall) gives rise to somatic structures.



• The Visceral tube is suspended from the body wall by a mesentery. The space between the visceral tube and the body wall is the coelomic cavity. This cavity is subdivided by the muscular diaphragm into thoracic and abdominopelvic cavities.



• Visceral structures include the digestive tract (and its organ derivatives), the lungs and most components of the urinary* and reproductive systems*. The heart has a different origin, but comes to lie ventral to the visceral tube within the thoracic cavity.

* The urogenital organs are unique in that they are morphologically visceral but somatic in location.

• The somatic components of the body wall include the integumentary, musculo-skeletal and central nervous systems.



• Since both somatic and visceral derivatives must be nourished and innervated, it is evident that the cardiovascular and nervous systems must have both somatic and visceral components.



• The somatic body wall may be subdivided into epaxial and hypaxial regions with reference to the vertebral column (= axis). The muscles (and skin) between the lateral (transverse) processes and the dorsal (spinous) processes are epaxial tissues while the muscles (and skin) between the lateral (transverse) processes and the ventral midline are hypaxial tissues.