Part Three
Splanchnology

Splanchnology （内脏学） includes the digestive，respiratory，urinary and genital systems．The organs within the four systems are termed the viscera（internal organs），which are mainly located in the thoracic，abdominal and pelvic cavities．The primary organs of the digestive and respiratory systems develop from the endoderm，while the main organs of the urinary and genital systems are derived from the mesoderm．Visceral organs play an important role in the metabolism and reproduction．Some of viscera have endocrine functions and secrete hormones．

In order to describe and identify the position of the viscera，landmark lines on the thorax and abdomen were made（Figure 3.1）．The major lines on the thorax are the anterior median line，midclavicular and subscapular lines．The anterior median line is the vertical line which passes through the middle of the sternum．The midclavicular line is the vertical line through the midpoint of the clavicle．The subscapular line is the vertical line through the inferior angle of the scapula．The abdomen is divided into nine regions by two horizontal planes and two vertical planes．The superior horizontal plane is named subcostal plane which passes through the inferior borders of the left and right costal arches．The inferior horizontal plane is named intertubercular plane which passes through the tubercles of the left and right iliac crests．The vertical plane passes through the midpoint of the inguinal ligament．The nine regions include the central umbilical region with lumbar regions to the right and left of it．Superior to the umbilical region is the epigastric region with hypochondriac regions to its left and right．Inferior to the umbilical region is the hypogastric region with iliac regions to its left and right．In the clinical，regions are simply divided into upper left，upper right，lower left and lower right quadrants through the horizontal and vertical umbilical planes（Figure 3.2）．