The posterior limb is a section of the internal capsule, which is a structure in the human brain that's composed of white matter. Also known as the crus posterius and the occipital part of the internal capsule, the posterior limb is located behind the genu and in between the thalamus and the lenticular nucleus. The posterior limb contains corticospinal fibers, which are a type of nerve fiber that originate in the cerebral cortex and extend to the spinal cord. Only the rear two-thirds of the posterior limb contain corticospinal fibers. One-third of the back portion of the posterior limb contains four types of fibers: sensory fibers, optic radiation fibers, acoustic fibers, and fibers that ravel between the occipital and temporal lobes to an area of the pons called the neclei ponti.
The deep brain structure known as the internal capsule separates the the lenticular nucleus from the thalamus and the caudate nucleus. The caudate nucleus is located in the deep brain structure called the basal ganglia and plays a role in learning and memory. The thalamus sits near the center of the brain on top of the brain stem, is bulb-shaped in humans and has multiple functions. A primary function of the thalamus is relaying information from all of the body's sensory systems, except the olfactory system, to the correct area of the brain for processing. The lentiform or lenticular nucleus is located in the basal ganglia and is made up of two basal ganglian structures called the putamen and the globus pallidus.
The internal capsule appears to be shaped in a "V" when cut both transversely, which means to divide into upper and lower portions, and coronally, which means to divide into front and back portions. The bend in the internal capsule's v-shape is called the genu. The nerve fibers found in the genu are called genticulate fibers and originate in the cerebral cortex, which is the outermost layer of neural tissue in the human brain.
When cut transversely, the interior capsule can be divided into five basic parts. The first anatomical landmark is the genu. The anterior limb, which also known as the crus anterius, of the internal capsule sits in front of the genu and between the lenticular nucleus and the caudate nucleus's head. The posterior limb sits behind the genu and between the lenticular nucleus and the thalamus.
The retrolenticular portion is below the lenticular nucleus. The fifth part of the internal capsule is the sublenticular portion and it sits under the lenticular nucleus. The sublenticular portion is consistent with Brodmann Area 41, which is the primary auditory cortex and is responsible for processing aural information.