NEEVE-TISSUE. 281 



takes place. The bundles of nerve-fibers, leaving the ganglia and entering 

 the central tubular gray investment of the brain, are considered as the pro- 

 jection system of the second order. This system is composed of two portions. 

 One for the impulse of voluntary muscle action, arises from the corpus 

 striatum and the nucleus lenticularis, penetrating the pedunculus cruris 

 cerebri ; the other portion is the route of reflex motion, and takes its origin 

 from the thalamus opticus, the corpora quadrigemina, and the corp. genicula- 

 tum internum, running into the tegmentum cruris cerebri. 



The tubular gray matter gives rise to the peripheral nerves, which are 

 greatly increased in number, as compared with their reduction in the ganglia. 

 The peripheral nerves represent the projection system of the third order. The 

 accumulations of nerve elements in the tubular gray matter are termed its 

 nuclei, and this gray matter itself lies bare on the base of the brain in the 

 lamina perforata posterior and the infundibulum. 



The cerebellum is independent, to a certain degree, of the projection 

 systems of the brain, though connected by the crura cerebelli with the cortex 

 cerebri, and probably by the crura cerebelli ad pontem. It connects with the 

 spinal cord through the fasciculi gracilis and cuneiformis and the restiform 

 bodies. 



The medulla oblongata connects the brain with the spinal cord ; in this 

 formation the projection system of the second order is reduced to its simplest 

 form, as observed in the spinal cord. Both halves of the medulla oblongata 

 are connected by the pyramidal decussations, and both contain a number of 

 gray nuclei, the superior and inferior olivary bodies and the nucleus of the 

 pyramis. 



The cortex of the brain has a common form of stratification, from which, 

 however, deviations are found in the occipital extremity, in the cortex bound- 

 ing the fossa Sylvii, in Ammon's horn, and in the olfactory bulb. 



There are five strata of the cortex cerebri in man, which are as follows : 



(a) The most superficial layer, which consists mostly of connective tissue, 

 and of a few small ganglionic elements and delicate nerve-fibrillae ; 



(b) The second layer is marked by a large number of small, multipolar 

 ganglionic elements ; 



(c) The third and broadest layer contains multipolar ganglionic elements, 

 decidedly surpassing in size those of the second layer. Their shape is either 

 pyramidal or fusiform, with the longitudinal direction vertical to the brain 

 surface. Their upper projection divides into a delicate reticulum ; the lower 

 passes without division toward the white substance ; 



(d) The fourth layer contains small globules, with very delicate offshoots : 

 these, possibly, may be only connected with the sensory nerves ; 



(e) The fifth layer holds spindle-shaped ganglionic elements, which lie 

 parallel to the surface of the brain, and have undivided offshoots. Meynert 

 considers them to be the intercalated cells of the system of association. 



In the occipital extremity there are eight layers ; the third typical layer is 

 wanting, but the granular formation is composed of three layers. In the 

 cortex, bounding the fossa Sylvii, the fifth layer is markedly developed, pro- 

 ducing the claustrum. The cortex of the Ammon's horn has no granular 

 layer, while the motor elements of the second and third typical layers are 

 very abundant. The cortex of the olfactory bulb in its upper portion is cov- 

 ered with a white layer, and exhibits from below upward : a layer of non- 

 medullated nerve-fibers, a layer of the glomeruli olfactorii, a layer of 



