59^ 'Journal of Comparative Neurology and Psychology. 



These are the chief anatomical contributions known to the writer 

 which give positive evidence as to the character of the root bundle 

 in question, Merkel and Krause as cited by Kolliker (1896, pp. 289, 

 292) described the cells of origin as bipolar cells, the dendrite 

 descending, the axone ascending. Edinger considers that the cells 

 of origin in lower vertebrates lie in the large-celled nucleus tecti. 

 P. Ramon (1904) has found the cells in the pigeon both in the nucleus 

 tecti near the median line and also far laterally in the tectum, as 

 Wallenberg found them in the duck. Bechterew (1887, 1899) ex- 

 presses his adherence to Meynert's view that this bundle joins the 

 sensory root. Held (1893) states that a part of the motor root 

 arises from the locus coeruleus and the cell-column in the mesen- 

 cephalon. In the human foetus these cells stained by the Golgi silver 

 method show numerous branching dendrites. Others, as Miss Sabin 

 (1907), have expressed themselves as unable to determine whether 

 the mesencephalic root leaves the brain with the sensory or the motor 

 root. 



Merkel (1874) described this as a trophic root and this view was 

 supported by Mendel (1888) on the basis of a case of hemiatrophia 

 facialis. The facts which Mendel brings fonvard will be referred to 

 later on. Bregmann (1892) found that cutting the motor branch 

 of the trigeminus caused degeneration of the motor root and the 

 mesencephalic root. 



Since the prevailing view at the present time is that the radix 

 mesencephalica is a motor root it will be well to summarize the evi- 

 dence thus far offered in support of this view. 



1. The fibers arise from cells in the locus coeruleus and corpora 

 quadrigemina. 



2. The fibers degenerate do^Amward after destructive lesion in the 

 tectum mesencephali of birds, 



3. The fibers pass close by the motor nucleus of the trigeminus in 

 mammals and according to most authors join the motor root to leave 

 the brain. Since the motor root is independent of the sensory root 

 and ganglion the fibers are presumed to be motor fibers, 



4. The fibers degenerate along with the motor root after cutting 

 the motor ramus. 



