To solve this problem, we need to identify the type of joint present between the atlas and axis vertebrae.$\newline$Let's analyze the options:$\newline \bullet$Cartilaginous joint: These joints are connected entirely by cartilage and allow more movement between bones than a fibrous joint but less than the highly mobile synovial joint.$\newline \bullet$Synovial joint: These are the most common and most movable type of joint in the body of a mammal. They are characterized by a synovial cavity filled with synovial fluid.$\newline \bullet$Saddle joint: A type of synovial joint where one of the bones forming the joint is shaped like a saddle with the other bone resting on it like a rider.$\newline \bullet$Fibrous joint: These joints are connected by dense connective tissue consisting mainly of collagen. They are fixed or immovable joints.$\newline$Now, let's focus on the pivot joint between the atlas and axis:$\newline \bullet$The atlas (C1) and axis (C2) are the first two cervical vertebrae in the spine.$\newline \bullet$The pivot joint between them allows for the rotation of the head.$\newline \bullet$This type of joint is a synovial joint, specifically a pivot joint, which allows for rotational movement.$\newline$Therefore, the correct answer is Option 2: Synovial joint.