PRIMITIVE SEGMENTATION OF THE VERTEBRATE BRAIN, A457 
Primitive Segmentation of the Vertebrate 
Brain. 
By 
Bertram H. Waters, A.B., 
H. M. Fellow in Biology. 
With Plate XXVIII. 
In 1828 Von Baer (26) observed various symmetrical folds 
in the hind-brain of the Chick, but only recently has their 
segmental value been appreciated. Much later they were 
seen by Remak (23) and Dursy (5), the former pointing out 
their intimate relation to the cranial nerves. In 1875 Dohrn 
(6) showed the segmental relations of these folds to the meso- 
blastic somites, and compared them to the segmentation of an 
insect. In 1876 Foster and Balfour (7), and a year later 
Mihalkovics (20), inclined to consider them as the purely 
mechanical results of mesoblastic pressure; but later histo- 
logical investigation of their structure seems to render such a 
position untenable. However, Balfour (2) says, in speaking of 
these constrictions in the hind-brain in the Chick, ‘‘ The 
sides become marked by a series of transverse constrictions, 
dividing it into lobes which are somewhat indefinite in number. 
The first of these remains permanent, and its roof gives rise to 
the cerebellum. It is uncertain whether the other constric- 
tions have any morphological importance. More or less 
similar constrictions are present in Teleostei. In Elasmo- 
branchii the medulla presents on its inner face at a late period 
a series of lobes corresponding to the roots of the vagus and 
VOL. XXXIII, PART 1Y.—NEW SER. Es 
