4 62 MR. YOUATr’s VETERINARY LECTURES. 
the brain or its membranes, and particularly in the direction of 
the great divisions or sinuses. This membrane consists of many 
laminae, and it is lacerated with much difficulty. 
The manner in which it covers the Brain. —The dura mater 
completely envelops the brain, but does not enter into any of its 
sinuosities or cavities ; it accompanies the optic nerve out of the 
cranium; and a prolongation of it, but singularly modified, as I 
shall have hereafter to describe, and no longer adhering to the 
bone, passes through the foramen magnum, and encloses the 
spinal marrow^ through its whole extent. 
The Longitudinal Sinus. —The dura mater dips deep into the 
scissure between the lobes of tlie brain, and that in a very curious 
manner. When it arrives at the central scissure on either side, 
it splits into two laminae, or collections of laminae. One of them 
passes over the scissure, and binds the lobes together ; the other 
runs deeply into it on one side, lining, as it were, the lobe on that 
side, and then being suddenly inflected or turned at the bottom 
of the scissure, it climbs up the other side of the sulcus to reach 
the external transverse portion, and thus forms a triangular 
cavity—the longitudinal sinus—the reservoir of the superficial 
venous blood of the brain, as will be hereafter more fully ex¬ 
plained. 
The Falx. —These laminae approximate to each other as they 
descend between the lobes forming the apex of this inverted tri¬ 
angle ; and at length uniting, pierce yet more deeply, under the 
denomination of the falx in the human being; but from the flat¬ 
ness of the brain of the quadruped it is much less developed, 
and scarcely deserves the name of a falx or scythe. A similar 
division and prolongation of this membrane is observable at the 
tentorium, dipping down beneath the bony part in the form of 
an irregular but narrow fringe. This duplicature of the dura 
mater is particularly extended in some animals that have not a 
bony tentorium. See this cranial cavity of the sheep, how per¬ 
fectly it is partitioned into distinct chambers by these mem¬ 
branous curtains. In some quadrupeds, however, the falciform 
process of the cerebellum is altogether wanting. 
The manner in which the proper falx and the tentorium meet 
each other at right angles, and the support they give to each 
other, and the method by which both are rendered tense and 
effective, are worthy of observation. The lateral sinuses are like¬ 
wise constructed of the laminae of the tentorium ; and the sphe¬ 
noidal and cavernous sinuses are formed from the splitting of the 
dura mater. 
The Dura Matei' in other Domesticated Animals. —I do not 
know of any considerable difference of structure in this mem- 
