Sclera in lobe-finned fishes, various reptiles, and birds. The ring has disappeared in many groups, including living amphibians, some reptiles and fish, and all mammals. The eyes of all non-human primates are dark with small, barely visible sclera. The collagen of the sclera is continuous with the cornea. From outer to innermost, the four layers of the sclera are: The sclera is opaque due to the irregularity of the Type I collagen fibers, as opposed to the near-uniform thickness and parallel arrangement of the corneal collagen. Moreover, the cornea bears more mucopolysaccharide (a carbohydrate that has among its repeating units a
Development of the human cerebral cortex in this area is where neurons, that are created in the ventricular zone, migrate through in order to reach the cortical plate. This zone is only present during corticogenesis and eventually transforms into adult white matter. The ventricular and subventricular zones exist below the intermediate zone and communicate to other zones through cell signalling, also creating neurons destined to migrate to other areas in the cortex. The marginal zone, along with the cortical zone, make up the 6 layers that form the cortex. This zone is the predecessor for layer 1 of the cortex. Astrocytes form an outer limiting membrane