It is absent in marsupials and monotremes, and in humans it contains about 300 million axons.  
Developed from the lamina terminalis, this structure consists of the rostrum, an enlarged and posterior splenium, the body, the anterior genu, and the ventrally directed rostrum, forming a semicircle when bisected. It is absent in marsupials and monotremes, and in humans it contains about 300 million axons.  Its absence during development is responsible for Aicardi syndrome. Alien hand syndrome can result from a treatment of last resort in epilepsy which involves bisection of this structure, which also leads to inability to read words seen from the left eye. FTP, name this structure of the brain that connects the two hemispheres of the cerebrum.
Developed from the lamina terminalis, this structure consists of the rostrum, an enlarged and posterior splenium, the body, the anterior genu, and the ventrally directed rostrum, forming a semicircle when bisected.
corpus callosum