MENIXGES. 351 



violet by tincture of iodine and sulphuric acid, and therefore are related to 

 amyloid. These corpuscida amylacea are found almost always in the 

 walls of the ventricles of the brain, and also in many other places both in 

 the gray and white substance and in the optic nerve. They have a homo- 

 geneous capsule with occasional processes, composed of neuroglia cells 

 transformed by amyloid infiltration. 



MENINGES. 



The meninges are connective tissue membranes investing the central 

 nervous system. They are usually divided into three layers, the dura 

 mater, arachnoid, and pia mater. 



The dura mater spinalis, or dura mater of the cord, consists of com- 

 pact fibrous connective tissue with many elastic fibers, flat connective 

 tissue cells and plasma cells. Its inner surface is covered by a layer of 

 flat cells forming a mesenchymal epithelium. It has few nerves and blood 

 vessels. The dura mater cerebralis or dura mater of the 

 brain, includes the periosteum of the inner surface of the 

 cranium and consists of two lamellae. The inner is like 

 the dura mater of the cord but contains more elastic 

 fibers; the outer corresponds with the periosteum of 

 the vertebral canal and consists of the same elements 

 as the inner layer, but its fibers run in a different direc- 

 tion. It contains many blood vessels, some of which 

 extend into the cranial bones. The very large thin- FIG. 40 6. ACERVULUS 



111- i-ll 11 1 mi 1 FROM THE PlNEAL 



walled veins of the dura are called sinuses. Ihe dura BOOT or A WOMAN 



SEVENTY YEARS 



has many nerves, some ending freely and others supply- OLD. x s- 



ing the vessels. 



The arachnoid of the cord and brain is but loosely connected with the 

 dura, being generally limited externally by a mesenchymal epithelium. 

 Between the arachnoid and the dura there is a capillary cleft containing 

 a very small amount of fluid. This subdural space in the rabbit and dog 

 is in communication with the deep cervical lymphatic vessels and glands, 

 with the lymphatic spaces around the peripheral nerves, with the lymphatic 

 vessels of the nasal mucosa, with the tissue spaces in the dura, and with those 

 around the arachnoid granulations. 



The arachnoid granulations [Pacchionian bodies] are elevations or 

 outpocketings of the arachnoid in definite places, especially along the sides 

 of the superior sagittal sinus. Covered by a thin portion of the dura and 

 by the endothelium of the vessel, they project into the cavity of the sinus. 



The subarachnoid space between the arachnoid and the pia mater, is 

 traversed by strands and layers of tissue and bounded by mesenchymal 



