Question

how are alary muscles arranged in pericardial sinus of cockroach

Answer 1

The dorsal diaphragm is a fenestrated membrane which separates the upper pericardial sinus from the lower perivisceral sinus. It consists of connective tissue with associated muscles which are called alary muscles because in some insects, for example cockroaches, they resemble wings projecting laterally from the dorsal vessel of each abdominal segment. Although sometimes mistakenly thought to play a key role in heartbeat, the alary muscles are more properly called muscles of the dorsal diaphragm. Whereas the myocardium is specialized to contract rapidly and constantly, the ultrastructure of the alary muscles indicates infrequent and slow contractions. The muscles associated with the dorsal diaphragm may likewise be arranged in a loose network, as in Lepidoptera, or arranged like a weave surrounding the dorsal vessel, as in some Diptera; the functional role of these muscles is difficult to determine.