154 REPORT—1840. 
for we have there fcetal placental vessels, resembling the branchial ves- 
sels of aquatic animals, covered by a prolongation of the inner coat of 
the vascular system of the mother, and hanging in a cavity filled with 
maternal blood. 
On the Anatomy of the Medulla Oblongata. By Dr. Joun Ret. 
The object of this communication was to point out the relative posi- 
tion of the motor and sensitive columns of the spinal chord, as they 
pass through the medulla oblongata and pons Varolii, and the attach- 
ment of the different motor and sensiferous nerves to these columns. 
Dr. Reid produced preparations of the medulla oblongata to show that 
the decussation of the pyramidal bodies is formed by the greater, and 
in some cases nearly the whole, of the fibres constituting each of these 
eminences passing into the posterior part of the middle column of the 
opposite side. None of these decussating fibres run into the anterior 
column of the opposite side, nor is there any decussation in the me- 
dulla oblongata besides this. On tracing the column which is con- 
nected with the olivary body, and which may be termed the olivary 
column, we find that as it passes downwards it approaches closely to 
the anterior median fissure immediately below the decussation of the 
pyramidal columns, and affords attachment to many of the roots of the 
motor nerves. On tracing this olivary column upwards it is found to 
expand over the olivary body, affording origin to the hypoglossal and 
abducens along its anterior margin, and to the porta dura along its 
posterior margin. Part of this column passes upwards to the corpora 
quadrigemina, affording origin to the smaller root of the fifth and to the 
trochleator. Dr. Reid also pointed out how the spinal accessory, and 
part of the filaments of the par vagum, may be connected with the 
motor column. 
On the Mechanical Functions of the Ear. By Dr. Sym. 
The following is a general summary of the contents of this paper. 
1. The external ear protects the membrana tympani, and contributes 
to a knowledge of the direction of sounds. 
2. The membrana tympani is a passive medium of communication 
of vibrations, and the impulses of the air draw its apex outwards. 
3. The ossicula of the tympanum form a system of levers, by which 
the extent of the undulations falling on the membrana tympani is di- 
minished, whilst their momentum is preserved. 
4. Vibrations communicated from the larynx through the temporal 
bone to the styloid process of the malleus and long crus of the incus, 
have their extent zxereased, whilst their momentum remains the same. 
5. The base of the slopes is drawn outwards by the impulses of the 
air, and performs the action of a piston. 
6. The muscles of the tympanum antagonize the impulses, and re- 
store the membranes and bones to their quiescent positions. 
