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 during neurogenesis at mouse E10.5 to E12.5. Of the six layers found within the cortex, "layer 1 is the most superficial layer of the cortex...composed of Cajal-Retzius neurons and pyramidal cortex cells." This layer is unique in the aspect that these cells migrate to the outer edge of the cortex opposed to the migration experienced by the other 5 layers. Layer one is also characterized by expression of reelin, transcription factor T-box brain 1, and cortical migratory neuronal marker. The second and third layers, or the External Granular layer and External Pyramidal layer respectively, are formed around mouse E13.5 to