Fig. 4 The anatomy of the thoracic region and stomach of crayfish. (A) Angled view of a 3D model reconstructed from MRI data. The anatomical structures identified and displayed within the thoracic region are the bilateral antennary arteries (AnA), the ventral artery (VA), the antennal glands (AG), the anterior part of both lobes of the hepatopancreas (He) and the foregut, including the stomach (St) and esophagus (Es). The exoskeleton was made transparent for better illustration. (B) A side view of the same model. Cutaway of antennal gland and added transparency to the hepatopancreas reveal internal structures. The bladder (Bl) almost completely encloses the remaining tissue (iAG) of the antennal glands. The hepatopancreatic tubules (HeT) inside the hepatopancreas and the duct that connects them to the stomach can also be seen. Insets in A and B: Red boxes indicate the area displayed beneath in the enlargements. (C) Sagittal section of the stomach. The internal structures identified and displayed within the foregut are the esophagus (Es), the cardiac stomach (CSt), the lateral (LT) and medial tooth (MT), the ventrolateral cardiac filter (VCF), the cardio-pyloric valve (CpV), the pyloric stomach (PSt) and the dorsal valve (DV). (D) Coronal section of the (cardiac) stomach. Identified and displayed structures are the lateral teeth (LT), the esophagus (ES) and the cardio-pyloric valve (CPV). The external tissue surrounding the interior of the stomach is displayed as a uniform structure in bright yellow color. Other organs were removed for means of clarity. Insets in C and D: Dark planes indicate the positions at which the portions of the crayfish displayed beneath in the enlargements were cut open. All scale bars, 1 cm. Data in A–D were reconstructed from images acquired in the same crayfish (mass 31.8 g) that was injected with 60 µl of a 120 mmol l^–1 MnCl₂ solution and scanned at T_R=1.5 s, T_E=17.6 ms; matrix dimensions: 256x256, field of view=5.12 cmx5.12 cm, number of averages=20, slice thickness, 200 µm; voxel size, 200x200x200 µm; acquisition time (total), 12.5 h.