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.
Skull. The human skull consists of about 22 to 30 single bones which are mostly connected together by ossified joints, so called sutures. The skull is divided into the braincase (cerebral cranium) and the face (visceral cranium). Its main task is the protection of the most important organ in the human body: the brain.he skull base is the caudal boundary of the cerebral cranium. Looking at it from the inside it can be subdivided into the anterior, middle and posterior cranial fossae. The skull base comprises parts of the frontal, ethmoid, sphenoid, occipital and temporal bones.