Dorsal Diaphragm

The heart lies upon a thin dorsal diaphragm, a sheet stretching across the anterior end of the abdominal cavity in segments three to seven. The membrane holds five pairs of fan-shaped bundles of fine muscle fibers that attach laterally to the anterior ends of the tergal plates of each segment. The fibers spread towards the heart where the fibers break up into many smaller branching fibrils. The pericardial cavity, the space containing the heart, lies above this dorsal diaphragm. The lateral borders of the diaphragm are not attached to the walls of the cavity between the attachment points for the muscles leaving gaps. Hemolymph enters the pericardial

Dorsal Diaphragm

Dorsal Diaphragm

Ventral Diaphragm

Figure 6.1. The Hemocoel. The hemocoel (black), cut horizontally on the half shell, is divided into three horizontally arrayed intercommunicating compartments: a dorsal pericardial sinus, the space surrounding the dorsal longitudinal vessel or heart, a middle perivisceral sinus surrounding the gut or intestine, and a ventrally placed perineural sinus overlying the ventral nerve cord. A dorsal diaphragm (white line), is a sheet of tissue that is incomplete in many places but separates the pericardial sinus from the perivisceral sinus. In a similar fashion, the ventral diaphragm (white line), also incomplete in places, separates the perivisceral sinus from the perineural or ventral sinus.

Ventral Diaphragm

Figure 6.1. The Hemocoel. The hemocoel (black), cut horizontally on the half shell, is divided into three horizontally arrayed intercommunicating compartments: a dorsal pericardial sinus, the space surrounding the dorsal longitudinal vessel or heart, a middle perivisceral sinus surrounding the gut or intestine, and a ventrally placed perineural sinus overlying the ventral nerve cord. A dorsal diaphragm (white line), is a sheet of tissue that is incomplete in many places but separates the pericardial sinus from the perivisceral sinus. In a similar fashion, the ventral diaphragm (white line), also incomplete in places, separates the perivisceral sinus from the perineural or ventral sinus.

cavity through these gaps as they impose little resistance to flow. Muscles as well as the tracheae may occur together in this gap region (see Tracheae below). Sometimes muscles cross the hemo-coel from one side of the hemocoel to the other; some muscles even traverse the dorsal diaphragm just below the heart. These muscles contract and compress the abdomen and its contents. Rhythmical movements of the dorsal diaphragm pulsate to ripple the diaphragm in a forward direction and help propel hemolymph forward.

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