ORGANS OF THE BODY. 597 



met with in the grey matter of the spinal cord ( 293). Nay, further, 

 the ramifying cellular processes are also seen here sinking into the latter. 

 But though the cortex presents this general plan of structure, there are 

 nevertheless local deviations from it. 



In the first place, at the point of the posterior lobe, in the neighbour- 

 hood of the sulcus hippocampi (a spot investigated long ago by Clarice}, a 

 number of anomalous white streaks present themselves in the cortical por- 

 tion. Meynert regards this part as made up of eight layers. The first 

 two of these conform to Nos. 1 and 2 of our fig. 562. The third stratum 

 lacks the large pyramidal cells, but presents in their place granules. 

 Under these there appear, as fourth layer, those scattered pyramidal 

 cells already mentioned, but very sparsely and at great intervals from one 

 another. As a fifth layer, we find granules again, as in the third. The 

 sixth resembles the fourth in having again scattered pyramidal bodies. 

 On this there follows another granular layer. The eighth and last layer, 

 finally, consists of ordinary fusiform cells (fig. 562, 5). 



The cornu ammonis presents the same difference of appearance. It 

 was first studied by C. Kupffer in the brain of the rabbit, and later by 

 Arndt and Meynert in the human being. 



According to the first of these observers, the structure is complicated, 

 but allied to that of a cerebral convolution. The cornu ammonis presents 

 under its most superficial layer of nerve fibres another so-called molecular 

 stratum of grey matter, which contains in its deeper portions a series of 

 closely-packed ganglion cells, one set of whose ramifying processes is 

 directed towards the centre, thus constituting a deeper streaked grey 

 lamina. Under this we next come upon a reticulated, then a second mole- 

 cular, and finally a stratum formed of closely-crowded " granules." 



According to Meynert, the grey cortical layer of the cornu ammonis in 

 man may be regarded as a thin covering layer without granules. At one 

 point alone namely, at the apex of the fascia dentata do these "granules" 

 appear in any great abundance. 



We turn now to the Iwlbus olfactorins, a remarkable piece of cerebral 

 substance, but ill developed in man. In many mammals it is, as is well 

 known, quite hollow. Its walls consist, if we will, of two groups of 

 laminae, an inner white and an external grey. The latter becomes more 

 and more highly developed as we approach the ethmoidal cells. 



Into the first the root bundles from the neighbouring parts of the brain 

 enter. Of these there are two first a strong root coming from the exter- 

 nal side, of which one-half seems to be a continuation of the anterior 

 inferior convolution of the brain, while the other thinner portion can be 

 followed into the corpus callosum ( Walter) ;. second, an internal weaker 

 root of the bulb, consisting of three bundles of fibres, one from the corpus 

 striatum, another from the chiasma nervorum opticorum, and the last from 

 thp pedunculus cerebri. In many points, however, Clarke's views differ 

 essentially from this sketch. 



If we now examine the walls from within outwards, the very complex 

 structure of the central organs presents itself to us here also. 



The cavity is lined with delicate ciliated epithelial cells, whose filiform 

 root processes penetrate into the strongly developed neuroglia of the sub- 

 stratum, with its roundish cellular equivalents. This latter is traversed 

 again at a slight depth by a set of fine longitudinal but medullated nerve- 

 fibres, which are a continuation of those of the root-bundles. Next to, and 

 probably derived from them, is to be found a stratum of nervous elements 



