The following short notes on the muscles of the Cockroach, aided by reference to the figures, will render the more noteworthy features intelligible. A very lengthy description, far beyond our space or the reader’s patience, would be required to explain in detail the musculature of the head, limbs, and other specialised regions. STERNAL MUSCLES OF ABDOMEN.--The _longitudinal sternal muscles_ (fig. 34) form a nearly continuous transversely segmented sheet, covering the ventral surface between the fore-edge of the second abdominal sternum and the fore-edge of the seventh. These muscles, in conjunction with the longitudinal tergal muscles, tend to telescope the segments. [Illustration: Fig. 34.--Muscles of Ventral Wall, with the Nerve-cord. × 5.] [Illustration: Fig. 35.--Muscles of Dorsal Wall, with the Heart and Pericardial Tendons. × 5.] The _oblique sternal muscles_ (fig. 34), which are very short, connect the adjacent edges of the sterna (2–3, 3–4, 4–5, 5–6, 6–7). They extend inwards nearly to the middle line, but, like the longitudinal sternal muscles, they are not developed beneath the nerve-cord. Acting together, the oblique sternal muscles would antagonise the longitudinal, but it is probable that they are chiefly used to effect lateral flexion of the abdomen, and that only the muscles of one side of the abdomen contract at once. The _tergo-sternal_ (or expiratory) muscles (figs. 35 and 36) form vertical pairs passing from the outer part of each abdominal sternum to the corresponding tergum. Their action is to approximate the dorsal and ventral walls, and thus to reduce the capacity of the abdomen. The first tergo-sternal muscle has its ventral insertion into the stem of the postfurca, and takes an oblique course to the first abdominal tergum. TERGAL MUSCLES OF ABDOMEN.--The _longitudinal tergal_ muscles extend from the fore part of each abdominal tergum, including the first, to the same part of the tergum next behind. They are interrupted by longitudinal spaces, so that the muscular sheet is less continuous than on the ventral surface, and has a fenestrated appearance. The direction of the fibres is slightly oblique. _Oblique tergal_ muscles, resembling the oblique muscles of the sterna, are also present. In the thorax the general arrangement of the muscles is greatly modified by the altered form of the dorsal and ventral plates, and by the attachment of powerful limbs.