594 MANUAL OF HISTOLOGY. 



In the outer portion of the cineritious substance is to be be found 

 another very interesting textural arrangement, again reminding us of the 

 retina (see below). A homogeneous connective-tissue boundary layer, 

 lying underneath the pia mater, and corresponding to the grey peripheral 

 lamina of the spinal cord, gives off internally, converging sustentacular 

 fibres (fig. 561 r), which may not unfrequently be followed through more 

 than half the depth of the whole grey matter (Bergmann, Schulze). 



299. 



There now remain for our consideration a few points in regard to the 

 histology of the cerebrum. 



The pedunculi cerebri, or crura cerebri ad pontem, consist of masses of 

 nerve-fibres, which pass partly from the medulla oblongata and cerebellum 

 to the brain, and partly from the latter into the medulla possibly. In 

 transverse section each crus is observed to be divided into two portions 

 by a crescentic band of grey matter, the substantia nigra. The most 

 inferior of these (" the base ") is crescentic, and the upper (" the cap ") 

 round. According to Meyjiert, it is motor fibres from the corpus striatum 

 and lenticular nucleus, or nucleus dentatus, which pass through this lower 

 part of the peduncles serving the purposes of voluntary motion. Through 

 the " cap," or upper portion, on the other hand, other fibres, arising in 

 the optic thalamus and quadrigeminal body, descend, which preside over 

 the reflex motions. Under the microscope the white matter of the crura 

 presents the ordinary central nerve-tubes and grey ganglionic corpuscles, 

 with numerous processes, which ramify largely, and pigmentary mole- 

 cules in their interior (fig. 305, 4, p. 314). 



Those structures which go by the name of the cerebral ganglia, namely, 

 the corpora quadrigemina, thalami optic?', nucleus dentatus, and corpora 

 striata, have up to the present received but little attention. 



The corpora qadrigemina possess, like the thalami, a white layer over- 

 laid with a zonal stratum of nerve-fibres. Underneath them the crura 

 cerebelli ad corp. quad, simply pass on to reach the cerebral hemispheres. 

 They are therefore incorrectly so called, for they are much more crura 

 cerebelli ad cerebrum. Laterally, there enter the corp. quad from 

 below the two lemnisci springing from the motor part of the medulla 

 oblongata, and traceable back to the same. Each of the ganglia sends 

 off two cords, the quadrigeminal arms, which are said to pass into the 

 system of the corona radiata. In the anterior of the quadrigeminal bodies 

 a root of the optic nerve, coming from the corpus geniculatum internum, 

 is said to terminate. The achievements of histology in this field -are still 

 very insignificant. Small cells have been recognised in the internal grey 

 substance with larger multipolar and fusiform ganglion corpuscles. The 

 latter are to be found in the deeper layers of the anterior bodies about the 

 aqueduct of Sylvius (Meynert). 



The optic thalami, we take it for granted, are already familiar to our 

 readers as regards form. Their posterior end has received the name of 

 the puluinar. Internally to it is situated the corpus geniculatum internum, 

 more posteriorly ; and externally the e.g. externum. Into the latter a 

 portion of the optic tract passes on its way to the pulvinar. The cap of 

 the crus cerebri is intimately connected with the thalamus. These are then 

 the newest views of Meynert ; but some years ago, J. Wagner came to 

 different conclusions in regard to the optic tract, and they will be probably 

 modified still by subsequent observations. An abundant corona radiata 



