The transverse mesocolon is a broad, meso-fold of peritoneum

Peritoneum

The peritoneum is the serous membrane that forms the lining of the abdominal cavity or the coelom — it covers most of the intra-abdominal organs — in amniotes and some invertebrates...

, which connects the transverse colon

Transverse colon

The transverse colon, the longest and most movable part of the colon, passes with a downward convexity from the right hypochondrium region across the abdomen, opposite the confines of the epigastric and umbilical zones, into the left hypochondrium region, where it curves sharply on itself beneath...

 to the posterior wall of the abdomen

Abdomen

In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

.

It is continuous with the two posterior layers of the greater omentum

Greater omentum

The greater omentum is a large fold of parietal peritoneum that hangs down from the stomach...

, which, after separating to surround the transverse colon, join behind it, and are continued backward to the vertebral column

Vertebral column

In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...

, where they diverge in front of the anterior border of the pancreas

Pancreas

The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...

.

This fold contains between its layers the vessels which supply the transverse colon.

Transverse mesocolon is a derivative of dorsal mesentery

Dorsal mesentery

The portion of mesentery attached to the greater curvature of the stomach is named the dorsal mesentery , and the part which suspends the colon is termed the mesocolon....

 in the embryo.

Contents

• 1- transverse colon
  Transverse colon
  The transverse colon, the longest and most movable part of the colon, passes with a downward convexity from the right hypochondrium region across the abdomen, opposite the confines of the epigastric and umbilical zones, into the left hypochondrium region, where it curves sharply on itself beneath...
  
   ( in the free margin )
• 2- middle colic vessels and their branches
• 3- lymphatics and lymph node
  Lymph node
  A lymph node is a small ball or an oval-shaped organ of the immune system, distributed widely throughout the body including the armpit and stomach/gut and linked by lymphatic vessels. Lymph nodes are garrisons of B, T, and other immune cells. Lymph nodes are found all through the body, and act as...
  
  s
• 4- autonomic
  Autonomic nervous system
  The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
  
   nerve fibers
• 5- extraperitoneal fatty tissue