The Glymphatic System and Subarachnoid Lymphatic-Like Membrane: Recent Developments in Cerebrospinal Fluid Research.

Background: Cerebrospinal fluid (CSF) circulates throughout the ventricles, cranial and spinal subarachnoid spaces, and central spinal cord canal. CSF protects the central nervous system through mechanical cushioning, regulation of intracranial pressure, regulation of metabolic homeostasis, and provision of nutrients. Recently, investigators have characterized the glial-lymphatic (glymphatic) system, the analog of the lymphatic system in the central nervous system, and described a fourth meningeal layer; the subarachnoid lymphatic-like membrane (SLYM)relevant to the CSF.

Bone histology in extant and fossil penguins (Aves: Sphenisciformes).

Substantial changes in bone histology accompany the secondary adaptation to life in the water. This transition is well documented in several lineages of mammals and non-avian reptiles, but has received relatively little attention in birds. This study presents new observations on the long bone microstructure of penguins, based on histological sections from two extant taxa (Spheniscus and Aptenodytes) and eight fossil specimens belonging to stem lineages (†Palaeospheniscus and several indeterminate Eocene taxa).