Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 53

The elasmobranch cranium encloses the brain, olfactory bulbs, and optic and otic organs. Similar to bony fish, the brain is composed of the telencephalon (forebrain); diencephalon (epithalamus, thalamus, and hypothalamus); and mesencephalon (with the cerebellar body and auricles and the medulla) (Northcutt 1977; Hofman 1999; Shuttleworth 2012).

The brains of elasmobranchs vary widely in shape and size. Some groups show an obvious asymmetry within the cerebellum, including rays (Myliobatiformes), requiem sharks (Carcharhinidae), and hammerhead sharks (Sphyrnidae). This asymmetry is notable on gross examination and should not be assumed to be pathological (Northcutt 1977). Cranial nerves are similar to other vertebrates.

The choroid plexus forms the cerebrospinal fluid (CSF); there is a large space rostral to the brain where this fluid can be collected. The electrolyte composition of CSF and plasma is different and regulated independently. The blood–brain barrier is different from other vertebrates in that the endothelium is permeable but there are tight junctions between glial cells (Bradbury 1979; Shuttleworth 2012).