SPINAL CORD 413 



Villiger (Brain and Spinal Cord, translated by Piersol, 1912). The form 

 of the cord at different levels is considered in works on gross anatomy. 

 In general, the white substance increases toward the brain, since the 

 cervical cord contains the fibers to and from all the lower levels in addi- 

 tion to those for the cervical region itself. In levels which supply the 

 nerves to the upper and lower limbs, there is a general increase in both 

 gray and white substances, producing the cervical and lumbar enlarge- 

 ments, respectively. The lower end of the cord tapers into the rudimen- 

 tary filum terminate. 



Adult Structure. The spinal cord and brain are surrounded by two 

 membranes or meninges, of which the outer is dense and fibrous, and is 

 known as the dura mater; and the inner is thin and vascular, forming the 

 pia mater. 



Curiously they are not called membranes, and the term meninx (in the singular) is 

 not employed in anatomy. They retain the ancient Arabic designation of "mother of 

 the brain," following, according to Hyrtl, a general Arabian tendency to name things 

 "mothers," "fathers," etc. (The vena cava was the mater venorum, and the pupil, the 

 filia oculi.) Carrying the figure further, the adjectives of double meaning, dura and 

 pia, were substituted for dense and thin. In the fifteenth century it was said that 

 these membranes were called matres because they produce the membranes surrounding 

 the nerves, the coats of the eye, and the periosteum of the skull, with which they 

 are continuous; but Hyrtl denies that the term has any such significance. 



The dura mater spinalis, or dura mater of the cord, consists of compact 

 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. 

 Anteriorly it is continuous with the dura mater of the brain at the foramen 

 magnum. It does not fill the vertebral canal, and is not continuous with 

 the vertebral periosteum. Around it externally there is a layer of vascular 

 fatty connective tissue; and internal to it there is a capillary cleft con- 

 taining a very small amount of fluid. This subdural space connects with 

 tissue spaces in the dura and with those which extend out in the peri- 

 neurium of the peripheral nerves. It communicates freely, but probably 

 indirectly, with the lymphatic vessels. 



The pia mater spinalis, as described by Stohr, is a two-layered sac. 

 The outer layer is covered on its free outer surface with a simple layer of 

 flat cells, which is lightly connected with the dura, and forms the inner 

 wall of the subdural space. The inner layer, or pia proper, is a delicate 

 and very vascular connective tissue, closely connected with the spinal 

 cord, into which it sends prolongations accompanying the blood vessels. 

 The arteries of the spinal cord are primarily two pairs, situated as shown 

 in Fig. 125, (p. 133) and in Fig. 424. One pair is ventral to the dorsal 

 roots, and the other is near the mid-ventral fissure; their branches supply 

 both the white and gray substance, and the collecting veins branch freely 



