MEDULLA OBLONGATA OR BULB. 447 
proceeds upwards on the surface of the medulla, The fascicles which carry up 
the line of the posterior nerve-roots on the surface of the medulla are the root- 
bundles of the spinal accessory, the vagus, and the glosso-pharyngeal nerves. These 
are attached along the bottom of a furrow which is the direct continuation upwards 
of the postero-lateral furrow of the cord, and therefore receives the name of the 
 postero-lateral furrow of the medulla. The root-bundles of these nerves differ, 
however, in so far that 
they are not all com- 
_ posed of afferent fibres 
_ -— Tenia thalami 
springing from gang- Loh neaiiene 
 lionie cells placed with- 
4 out and entering the pannel body 
medulla. Certain ot Prenat: __ Inferior quadri- 
them are purely efferent psominalybody, 
(spinal accessory roots), Valve of Vieussens 
— whilst others likewise © us Godan 
» contain a considerable Superior peduncle of Pontine part of floor 
~ numberof efferent fibres, SE Wy a ee ae a 
~ and are therefore to be the cerebellum : Eminentia teres 
regarded as mixed roots. =) woved superior 
7 By the antero-pos- Bixiee aensies . 
i terior and the antero- Area acustice Rostlformbady, 
lateral grooves, and also Trigonum vagi_ ——— BaD el Neel E 
by the two rows of nerve — Clava 
fascicles attached along 
the bottom of these fur- 
rows, the surface of the 
medulla on each side is 
divided into three dis- 
tricts, viz. an anterior, a 
lateral, and a posterior, 
similar to the surface 
) areas of the three 
~ columns on the side of the cord. Indeed, at first sight, they appear to be a direct 
- continuation upwards of these three portions of the cord; this is not the case, 
however, because the fibres of the three columns of the cord undergo a rearrange- 
~ ment as they proceed upwards into the medulla. 
; Anterior Area of the Medulla—Pyramid (pyramis)—The district between 
_ the antero-median fissure and the antero-lateral furrow, along the bottom of 
which the root-fascicles of the hypoglossal nerve issue from the medulla, receives 
the name of the pyramid. An inspection of the surface is sufficient to show 
that the pyramid is composed of a compact strand of longitudinally directed 
nerve-fibres. Tapering below, it expands and assumes a prominent appearance 
as it is traced upwards, and, finally reaching the lower border of the pons Varoli, 
it becomes slightly constricted and disappears from view by plunging into that 
portion of the brain. The two pyramids, separated from each other by the antero- 
median furrow, are the great motor strands of the medulla. 
Although the pyramid at first sight appears to be continuous with the anterior 
column of the cord, only a very small proportion of the fibres contained in the 
latter are derived from the pyramid. This at once becomes manifest when the 
lips of the antero-median fissure are thrust apart at the place of junction between 
the cord and the medulla. The pyramid is then seen to divide at this level into 
two parts, viz. a small portion composed of a variable number of the outermost 
fibres of the pyramid, termed the direct pyramidal tract, and a much larger portion 
situated next the antero-median fissure, called the crossed pyramidal tract. The 
direct pyramidal tract is continued down into the anterior column of the cord, 
and in this it. takes up a mesial position next the antero-median fissure. The 
crossed pyramidal tract is broken up into three or more coarse bundles, which 
sink backwards and at the same time cross the mesial plane, to take up a position 
C ‘cle 
EEE IS Rolandic tubercle 
Funiculus gracilis - 
Funiculus cuneatus 
Fic. 333.—Back VIEW OF THE MEDULLA, PONS, AND MESENCEPHALON OF 
A FULL-TIME HUMAN Fa@rTus. 
