4'52 THF BRAIN OF MAMMALS, BY TH. MEYNERT. 



gemina cease. It consists (1) of the connecting arm (pro- 

 cessus cerebelli ad cerebrum) expanded at the level of the 

 nates by the red nucleus of the tegmentum, the cells of which 

 disappear at the level of the testes ; (2) of the posterior longi- 

 tudinal fasciculi springing from the ganglion of the ansa pe- 

 duncularis (collar of eras) ; (3) Of a decussating origin from 

 the optic thalamus through the tract of the posterior commis- 

 sure ; (4) of a non-decussating origin from the optic thalamus, 

 forming the laminae medullares ; (5) of the possibly non- 

 decussating peduncle of the ganglion of the habenula ; (6) of 

 decussating fasciculi arising from the pineal gland ; (7) of the 

 loop (fillet) from the nates, the upper lamina ; (8) of the loop 

 (fillet) from the testes, the lower lamina ; (9) of the posterior 

 fasciculi of the crusta. 



Before the structure of the tegmentum forms the plexiform 

 region of the processus cerebelli ad pontem, which will be sub- 

 sequently described, an interweaving occurs in it at the level 

 of the nates, caused by a tract running peripherically into the 

 large root of the fifth pair. By this means this segment of the 

 tegmentum^ together with certain portions of the fasciculi of 

 the antero-lateral columns, enters into the same morphological 

 relations with the large root of the fifth pair as the medulla 

 obongata does> with the posterior roots of the spinal cord, 

 where in it the antero-lateral column is interlaced by the poste- 

 rior column of the spinal cord. The large cells of origin of the 

 descending roots of the fifth nerve, described at p. 447, which, 

 lying together in clusters, are imbedded in the outermost 

 border of the grey matter of the central cavities around the 

 aquseduct, give origin to a remarkable circle of marginal fibres 

 of the same, which may be collectively termed the strands of the 

 fifth pair of nerves. These strands of the fifth are arranged in 

 the form of a thin medullary vesicle (about 150 /z thick), sur- 

 rounding the aquseduct through almost the entire height of 

 the nates. Somewhat below the transverse diameter of the 

 wall of the aqueduct they become so transposed that instead 

 of being superjacent to one another they lie side by side, and 

 occupy a large space, whilst they diverge from each other like 

 a fountain, and interweave partly with the fasciculi of origin 

 of the spinal cord from the optic thalamus (excluding there- 



