188 QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE. 
number, but in some places occupying nearly the whole 
thickness of the mucous membrane. 
Process of Ossification—A. von Briinn (‘ Reichert’s 
Archiv,’ 1874, p. 1; ‘ Centralblatt,’ 1874, p. 727) gives the 
following summary of his conclusions on ossification from 
cartilage. 
(1) The cartilage-cells multiply and arrange themselves 
so as to form in the diaphysial part of the epiphysis- 
—cartilage bony row; in the epiphysial portion of the same 
and in the short bones, groups; both corresponding in di- 
rection to the medullary masses which afterwards find their 
way in. They increase in size towards the limit of bone, 
and thus enlarge the cavities in which they lie. The differ- 
entiation of the fundamental substance follows a different 
direction according as the bone is embryonic and unfit for 
use or is actually to be used. In the former case the car- 
tilage-capsule is very conspicuous around the enlarged cells, 
though it afterwards vanishes near the limit of bone. In the 
latter case the basic substance only remains hyaline where 
it immediately surrounds the rows of cartilage-cells and the 
capsules ; that which lies between the columns of hyaline 
substance becomes converted into an elastic fibrous tissue. 
(2) The cartilage-cells remain in the medullary spaces as 
medullary cells, where they become converted into osteo- 
blasts, and as such form bone. The greater part are con- 
verted into bone substance, but a certain number remain as 
bone-corpuscles. The canaliculi are formed by absorption. 
VII. Nervous System.—1. Cowrse of the Fibres in the Pos- 
terior Commissure of the Brain.—In Siebold and Kolliker’s 
‘ Zeitschrift fir Wissenschaftliche Zoologie,’ vol. xxiv, Heft 
3 (September 16, 1874), Dr. Paulowsky records the 
result of his investigations into the structure of the 
so-called posterior commissure of the brain. This body 
has been variously described; most authors, however, 
believing that its fibres run transversely between the 
two thalami optici, thus serving to connect the two 
hemispheres of the brain. According to Arnold, the 
commissure really consists of two factors, one of which 
belongs to the ‘‘Schleifenregion,” the other to the hemi- 
spheres. [The ‘“ Schleife” answers to the lemmniscus of 
Reil. The first factor probably answers to the commissure 
of Wernekinck.—Rep.] Luys has remarked a crossing of the 
nerve-fibres in the commissure. Meynert describes this 
structure as the crossing place of the anterior and posterior 
crura of the corpora quadrigemina, which, after crossing, 
pass over,into the tegmentum (“ Haube”’) of the crus cerebri, 
