Novel threadlike structures (NTSs) on the surfaces of mammalian abdominal organs have recently attracted interests regarding to their ability to transport fluid, enable cell migration, and possibly facilitate cancer metastasis. Nevertheless, histological studies of NTSs have been sporadic and often have inconsistent interpretations of the NTS internal structure. In this report, we provide a synthetic and consistent view of the NTS internal structure: the NTS is a loose bundle of fibrous stroma that form micro-sinusoids infiltrated with inflammatory cells. The fibroblasts are embedded in the stroma and mostly aligned along the major axis of the NTS. The sinusoids, which are in inconsecutive cross sections, have boundaries more or less delineated by extracellular fibers, partly surrounded by endothelial-like cells, or both. We compare these morphological features to other well-known connective tissues (i.e., trabecular meshwork and lymphatic capillary), and discuss the biomechanical and biological functions of NTSs based on their structural characteristics.