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.
The frontal bone is a bone of the skull found in the forehead region. It is one of eight bones that form the cranium, or brain case. The frontal bone plays a vital role in supporting and protecting the delicate nervous tissue of the brain. It gives shape to the skull and supports several muscles of the head.he frontal bone is a bone of the skull found in the forehead region. It is one of eight bones that form the cranium, or brain case. The frontal bone plays a vital role in supporting and protecting the delicate nervous tissue of the brain. It gives shape to the skull and supports several muscles of the head.