FIBROUS STRUCTURE. FOVILLE'S VIEWS. 



559 



they then turn inwards, and, joining with those of the opposite side, form the trans- 

 verse fibres of the corpus callosum. The corpus callosum is therefore regarded as 

 a commissure of the cerebral peduncles only none of its cross fibres spreading into 

 the convolutions, as is generally believed. 



b. The second set of fibres of the tegmentum, corresponding with the fasciculi 

 teretes and part of the posterior pyramids, run forwards near the middle line, along 

 the under side of the third ventricle and corpus striatum, through the grey matter 

 in front of the pons, to the anterior perforated space. The remaining part of the 

 posterior pyramid forms the taenia semicircularis, which, passing down in front of the 

 anterior pillar of the fornix, also reaches the perforated space. From this space 

 more fibres are reflected upwards on the sides of the corpus striatum to join the 

 corpus callosum. 



3. As dependencies of the posterior peduncular fibres, and connected with them at 

 the borders of the anterior perforated space, are : 



a. Several sets of longitudinal arched fibres, which embrace, in a series of rings, 

 the radiating peduncular system. These are the deep fibres of the taenia semicircu- 

 laris a somewhat similar baud beneath the outer part of the corpus striatum the 

 half of the fornix with the corpus fimbriatum the longitudinal fibres placed on the 

 upper and under surface of the corpus callosum, and those of the septum lucidum ; 

 and, lastly, two remarkable systems of longitudinal fibres one constituting the 

 entire white substance of the gyrus fornicatus (from end to end), also of its accessory 

 convolutions, and of the inner half of the marginal convolution of the longitudinal 

 fissure ; and the other, forming the white substance of the convolutions of the island 

 of lieil, and the adjoining half of the convolution of the Sylvian fissure. None of 

 the parts just named receive fibres from the radiating peduncular set. 



6. In connection with this system is a thin stratum of white fibres, found upon the 

 internal surface of the ventricles, aud prolonged through the transverse fissure into 

 the reticulated white substance covering the lower end of the gyrus fornicatus ; 

 whence, according to Foville, it extends, as an exceedingly thin layer of medullary 

 matter, all over the cortical substance of the hemisphere. 



c. The anterior commissure does not reach the convolutions, but radiates upon the 

 outer sides of the corpora striata and thalami. 



II. The fjrvij matter on the convoluted surface of the cerebrum is divided into two. 

 and in some regions into three strata, by interposed thin layers of white substance. 

 In examining it from without inwards, we meet with 1. A thin coating of white 

 matter situated on the surface, which on a section appears as a faint white line, 

 bounding the grey surface externally. This superficial white layer is not equally 



Fig. 382. SECTION OP Fig. 382. 



THE COKTICAL SlJB- 

 STANCE OF A CEREBKAL 



CONVOLUTION (from 

 Remak). 



In A, the parts are 

 nearly of the natural 

 size. To the right of the 

 figure, a and e are two 

 white, and b and / two 

 grey strata ; to the left 

 of the figure, an addi- 

 tional whi^e layer, ^di- 

 vides the first grey into 

 two, b and d. In B, a 

 small part of the cortical 

 substance of a con volution 

 is represented, magnified 

 to show more clearly the 



relative position of the strata ; a, superficial white layer ; 6, reddish grey layer ; c, inter- 

 mediate white layer; d, inner part of the outer grey layer ; e, thin white layer; /, inner 

 grey layer ; g, radiatiug white fibres from the medullary substance of the convolution 

 passing into the layers of the cortical substance. 



