Spider inside
The front part of the body (cephalothorax) is packed with muscles that help move the jaws and limbs. Muscles from limb and gut and carapace attachments are connected to the central endosternite, an internal non-chitinous skeletal plate. The mouth leads into fore gut which divides to encircle the brain ganglia from which the nerve cord runs back below the gut. The end of the fore gut forms a muscular stomach that pumps the liquid food up into the oesophagus and pharynx and moves it along the gut. Outgrowths (diverticula) extend from the midgut into the legs and fill much of the abdomen. The midgut and its diverticula ingest food and provide the spider with a considerable capacity for food storage. The hind gut has a sac into which excretory organs called malphigian tubules (the spider's 'kidneys') open, The abdomen also accommodates several different sorts of silk glands and the reproductive organs (ovary or testes). A tubular heart lies in the midline where it can be seen beating through the dorsal cuticle. The blood circulation is open - that is, the blood vessels from the heart into the body space, bathing the tissues and organs in blood, which gradually circulates back to the heart.
