The intraparietal sulcus (IPS), which is also known as the interparietal fissure, is a long crevice located in the parietal lobe of the human brain. The primary function of the intraparietal sulcus is related to directing eye movements, accurate reaching or arm extension, and visual attention, although it's also thought to play a role in understanding numerical symbolism and discerning the intent of others through visual cues. The IPS doesn't run in a straight line from its starting point to its ending point, instead it meanders from the lateral, or side, part of the parietal lobe to its termination point in the occipital lobe.
The outermost covering of the human brain is the cerebrum, and it's marked by many ridges called gyri, and fissures called sulci. The cerebrum is divided into right and left hemispheres by the great longitudinal fissure, which is also known as the medial longitudinal fissure, the longitudinal cerebral fissure, the longitudinal fissure, and the interhemispheric fissure. Both hemispheres of the brain are divided into four lobes: the frontal lobes located in the forehead region, the parietal lobes on the top and at the sides of the head, the temporal lobes on the sides of the head below the parietal lobes, and the occipital lobes at the back of the head.
Both the left and right parietal lobes contain an intraparietal sulcus. The interparietal fissure splits into two perpendicular lines at its lower end and, when connected to the postcentral sulcus at its upper end, forms an "H" shape that divides the parietal lobe into a superior and inferior lobule. In some brains the intraparietal sulcus is a continuous line, in others it's divided into two lines. In approximately two-thirds of brains the intraparietal sulcus begins at or near the middle of the postcentral sulcus, which is also located in the parietal lobe. The IPS travels down toward the upper part of the occipital lobe where it terminates in the transverse occipital sulcus.
The interparietal fissure has sections that extend horizontally and parts that extend obliquely. The intraparietal sulcus can have a varying number of branches projecting from it, which can point upwards or downwards. The uppermost downward pointing branch, which can extend from either the intraparietal sulcus or the postcentral sulcus, is called the primary intermediate sulcus. The downward pointing branch immediately below the primary intermediate sulcus, which extends from the intrapariteal sulcus, is called the secondary intermediate sulcus.