In open circulatory system, the blood (i.e. hemolymph) bathes the organs and tissues directly. Examples of animals with open circulatory system are arthropods and most mollusks. In closed circulatory system, the blood circulates within blood vessels throughout the body. Therefore, there is a distinction between blood and lymph. Examples of animals with closed circulatory system are annelids, few mollusks, and vertebrates.
Its main task is the protection of the most important organ in the human body: the brain. The brain is almost entirely enclosed by the cerebral cranium with the exception of the foramen magnum and other foramina at the skull base which serve as entry and exit point for blood vessels and cranial nerves. The braincase consists of the skullcap (calvarium) and the skull base.
A) The Neurocranium (Chondrocranium). The neurocranium is the portion of the skull that protects the brain and certain sense organs. In the Elasmobranchs (sharks and rays) it is composed of cartilage (chondrocranium), but in most other vertebrates, the cartilage is replaced by bone (endochondral or replacement bone).he dermatocranium forms most of the skull and functions as a protective shield for the brain. See the dermal armour of Amia, the bowfin, which sits on the cartilaginous neurocranium. In other animal groups the cartilage disappears and when you look down on the skull you are looking at the bones of the dermatocranium.