basement membrane morphology trait basal lamina morphology trait Any measurable or observable characteristic related to the shape, structure, color, or pattern of the sheet of extracellular matrix characteristically situated under epithelial cells, around muscles, nerves, capillaries, and fat cells, and situated between these elements and the underlying or surrounding connective tissue. Note: basal lamina and lamina reticularis (or of two basal laminae) compose the basement membrane. thus, in strict sense, the term basement membrane is different from and should not be confused with basal lamina. Trait.ontology VT:0004273