Sclera pass. The thickness of the sclera varies from 1mm at the posterior pole to 0.3 mm just behind the rectus muscle insertions. The sclera's blood vessels are mainly on the surface. Along with the vessels of the conjunctiva (which is a thin layer covering the sclera), those in the episclera render the inflamed eye bright red. In many vertebrates, the sclera is reinforced with plates of cartilage or bone, together forming a circular structure called the sclerotic ring. In primitive fish, this ring consists of four plates, but the number is lower in many living ray-finned fishes, and much higher
The Description of the Human Body He believed the heat of the heart somehow caused all movement of the body. Blood vessels he realized were pipes, he saw that veins carried digested food to the heart. (This was brought further by William Harvey. Harvey developed the idea of the circulation of the blood.) Descartes felt that an energetic part of blood went to the brain and there gave the brain a special type of air imbued with vital force that enabled the brain to experience, think and imagine. This special air then went through the nerves to the muscles enabling them to move. The Description of