This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
Apoplexy may also occur in other portions of the brain. It may occur in the pons (see Fig. 39). This produces two different sets of symptoms, according to its location, which is due to the fact that the fibres of the seventh or facial nerve, in their passage from the cortex to the face, decussate in the pons. If a small hemorrhage occurs into the upper portion of the pons, it will destroy the motor fibres to the face and the extremities of the opposite side. If, however, the hemorrhage is below the point of decussation, the side of the face on the side of the lesion will be paralyzed and the extremities of the opposite side, thus producing what is known as crossed paralysis, that is, a paralysis of the face on one side and of the extremities on the other.
Hemorrhages of the cortex are apt to be less in extent and more localized on account of the smaller size of the vessels affected. They either destroy or irritate the brain at the site of injury, and produce, if they involve certain areas of the brain, definite peripheral symptoms which serve to indicate the seat of lesion.
Fig. 39. - Diagram illustrative of crossed paralysis. A clot in the upper portion of the pons causes paralysis of the muscles of the face and extremities of the same side of the body. A clot in the lower portion of the pons causes paralysis of one side of the face and the extremities of the opposite side of the body.