556 Dynamic Theory. 



crus is much darker than that of any other part of the brain, and it is 

 here called the locus niger, or black spot. Fibres from this place pro- 

 ceed to the fornix, the great inferior longitudinal commissure of the 

 brain. After passing the corpora quadrigemina, the crura cerebri split 

 up and disappear. A part of the fibres, both motor and sensory, pass into 

 the lenticular nucleus, or anterior end of the corpus striatum (fig. 348, 349, 

 350, 354) ; a part of the sensory (but none of the motor) tracts pass into 

 the optic thalamus ; and the remaining motor and sensory tracts expand 

 into two thin bodies on the outside of and embracing the optic thalami. 

 These are called the internal capsules. Beneath the optic thalamus and 

 lying between it arid the internal capsule, is a group of cells apparently 

 sustaining to the capsule the same relation which the locus niger does to 

 the foot of the crus. This group of cells is called the sub thalamic re- 

 gion. The internal capsule, besides the main body of fibres from the 

 crus cerebri, receives fibres from this sub thalamic region and from the 

 thalamus itself. Of the internal capsule thus made up, the anterior 

 two- thirds consists of motor elements, and the posterior one-third of 

 sensory tracts embracing paths of sensation, including tactile sensation, 

 muscular sense, pressure, &c. , fibres which come up the spinal cord. 

 The fibres, after passing through the internal capsule, are joined by 

 others from the sub thalamic region and from the thalamus, and the 

 whole form what is called the corona radiata, a radiating crown which 

 sends its diverging fibres to every part of the cortex of the cerebrum. 



FIG. 273. Top view of Medulla and Basal ganglia 

 of the Horse. 



1. Upper end of the fig. shows the restiform bodies 

 on the posterior part of the medulla oblongata 



2. bection of the pons varolii, which becomes the 

 middle peduncle of the cerebellum (cerebellum is 

 removed ). 



3. Section of the posterior peduncle of the cere- 

 bellum, which is a continuation of the restiform 



4. Anterior peduncle of cerebellum. [ fibres 



6. t loor of the fourth ventricle. 



6. Valve of vieussens, stretching across between 

 the two anterior peduncles. 



7, 7. The rear bulbs of quadrigemina testes. 



8, 8. The anterior bulbs of " nates. 



9, 9. On the optic thalami. 



10. Corpus geuiculatum internum of the thalamus. 

 11. ^ externum " 



12. Corpus striatum. 

 13. Tenia semicircularis. 

 14. Pineal gland. 

 16. Its peduncle. 

 16. Foramen of Munro. 



17. Anterior pillars of the Fornix. [ facial. 



18. Sensory root of fifth nerve, trigeminum or tri- 

 19 Facial nerve (7th). 

 20. Auditory nerve (8th). 

 21. Glosso pharyngeal. 

 22. Pneumogastric or vagus nerve ( 10th). 

 Fia. 273. 23. Spinal accessory (llth). 



The peduncles, or crura cerebri, are separated from each other by a 

 fissure corresponding with the anterior fissure of the medulla oblongata. 

 It is called the interpeduncular fissure. The surface of the inner sides 

 of the peduncles is very much perforated by numerous blood vessels 



