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It consists of a series of chambers corresponding roughly to the leg-bearing segments, and lies in a blood-sinus formed by a pericardial membrane whence large alary muscles extend to the sides of the body.

The alary process of the premaxillary is small, concave posteriorly and vertical.

The high, narrow alary processes of the premaxillae extend dorsally about two-thirds of the height of the snout.

The alary process of the premaxillary is vertical and concave posteriorly.

The alary process of the premaxillary is small, vertical, and slightly concave posteriorly.