A STUDY OF THE CHOROID PLEXUS. 
(Abstract) 
BY WALTER J. MEEK. 
With the exception of scant references in the standard anatomies very 
little material treating of the choroid plexuses is available to the general 
student, and in fact many questions of interest concerning these struc- 
tures still remain unanswered. The object of the author has been to 
review the subject up to date and to give the result of his own investiga- 
tions. The work was carried on in the Neurological Laboratory of 
the University of Chicago. 
On account of their size and their accessibility the plexuses of the 
lateral ventricles were used exclusively. Mammalian material was 
studied from the following forms: white rat, rabbit, guinea pig, cat, 
dog, sheep, and man. 
The number of fixatives adapted to the plexuses is somewhat limited. 
Bouin’s fiuid, Carnoy’s solution, and acetic sublimate proved most satis- 
factory. For small animals the best results were obtained by fixing the 
entire brain. The period of fixation was shortened in all the fiuids. The 
usual methods of embedding in paraffin and sectioning were employed. 
Many stains Vv^ere used but the most satisfactory results were obtained 
with iron haematoxylin followed by acid fuchsin. 
The choroid plexuses of the lateral ventricles are due to an ingrowth 
of the pia mater pushing the mesial wall of the hemisphere into the 
ventricles. The neural wall is of course preserved but it consists only of 
a simple epithelium. The plexuses are then thin laminae covered with 
an epithelium, beneath which is a connective tissue stroma containing an 
extraordinarily rich netw'ork of blood vessels. 
In many animals the laminae are smooth but in others they are 
covered with projecting villi. Between these two extremes are to fee 
found all the intermediate gradations. The guinea pig, mouse, and raat 
possess plexuses that are smooth. In these forms there are prolonga- 
tions and projections of the folds, but the typical villi are absent. Villi 
are scarce in the chicken, duck, and pigeon, more abundant in the hog, 
while they reach a considerable development in the horse, ox, and 
especially among crocodiles and some of the selachians. In the rabbit 
the laminae are very irregularly folded but not villous. Villi are numer- 
ous along the free edge of the plexus in the sheep. In man villosities 
are found but the type is somewhat intermediate. 
It is generally believed that the choroid plexuses are largest in the 
embryonic state and that their volume diminishes as the brain reaches 
its full development. The model of His for the three month human 
