THE NERVES. 373 



tubercles have in the interior three distinct gray nuclei, one inter- 

 nal, external, and superior. The commissure (central) uniting 

 the optic tubercles, as well as the border found between them in 

 the third ventricle, also consists of gray substance. Still more 

 distinct and larger are the three gray nuclei of the striated bodies, 

 nucleus caudatus knticularis and tceniceformis. The stria cornea 

 consists of medullary matter, and only appears yellow when look- 

 ing through a vein. From the cerebral tubercles the great me- 

 dullary striae, only, pass out, the radiatio medullaris, fibres, 

 which, as they decussate with those of the corp. callosum, form 

 the hemispheres of the cerebrum. From the corp. striatum fibres 

 spread out towards both sides ; in front and behind fasciculi of 

 fibres go into the fornix, which they call the forceps. Those 

 which cover the lateral ventricles are called tapetum. The ante- 

 rior commissure consists, also, of white and gray matter. The 

 corpp. albicantia (with gray nucleus) are the commencements [?] 

 of the fornix ; they pass, as radix ascendens, into the columella 

 fornicis. Each right and left gives off a medullary plate, the 

 septum pellucidum, between which is the ventriculus septi pellu- 

 cidi, communicating with the third ventricle. The columella pass 

 into the body of the fornix. This divides into the crura, and 

 passes into the lateral ventricles. The peripheral part of the 

 fornix passes in an arch around the corp. callosum (gyrus forni- 

 catus), and terminates as, uncus, the hook. The fibres of the 

 crura form in the cornua of the ventricles, with others of the 

 corp. callosum, the pes hippocampi major and minor. The first 

 has two layers of medullary and two layers of gray substance ; 

 on it, as in the small, the gray is the cortical substance, covered 

 by medullary fibres. The fibrce explementorice here also fill up 

 the intervals between the fibres of the radiatio medullaris cerebri 

 of the peripheral fornix and of the corpus callosum. Medullary 

 lamince do not only pass from one convolution to another in an 

 arched manner, but a distinct mass also unites the anterior and 

 inferior lobes in the fossa Sylvii (fasciculus uneiformis. Reil.) 



624. The Membranes of the Brain. 



The brain and spinal cord are enveloped by three membranes 

 which pass, immediately, into one another at the foramen magnum. 

 Those of the spinal cord, see 628. The membranes of the 

 brain : 



1. The dura mater, s. meninx fibrosa, a fibrous sac, the exter- 

 nal rough surface of which is firmly attached to the internal cranial 

 bones, and here serves as periosteum; the internal, smooth, and 



