Figure 14-14.

Layers of the Meninges.

A, Brain, dog. The dura matter is a thick opaque layer. Here it covers the rostral (cranial) half of the brain and has been dissected away from the caudal half of the brain to expose the underlying leptomeninges. In old animals the dura mater often fuses with the periosteum of the calvaria, and at necropsy to expose the brain, it is usually removed attached to the calvaria. The leptomeninges are present, but because they are so transparent, they are barely visible on the surface of the caudal half of the brain between gyri. B, Spinal cord, horse. The dura mater is the thick opaque layer dissected from and lying to the right of the spinal cord. The leptomeninges (pia-arachnoid layer) are present (but not readily visible in this photograph) on the exposed surface of the spinal cord. Arrows indicate spinal nerve roots.

(Courtesy Dr. J.F. Zachary, College of Veterinary Medicine, University of Illinois.)