ME. J. L. CLAEKE ON THE OEEY SUBSTANCE OF THE SPINAL COED. 453 
I was desirous to know whether the posterior vesicular columns are present in the 
spinal cord of the lower Vertebrata. I found that in Birds, as in the larger Mammalia, 
the posterior cornua, near the middle of the dorsal region, are united along their inner 
borders, and form but a single mass, around which the gelatinous substance extends 
without interruption. Each on its outer side, where the caput cornu joins the cervix, 
is very much constricted, but again dilates as it extends forwards to be continuous with 
the anterior cornu, so that the entire grey substance has nearly the form of an hour-glass 
or goblet (see fig. 32, Plate XXIII.). Numerous cells of various shapes and of moderate 
size are scattered on each side and behind the canal, and are traversed by the posterior 
roots proceeding through the constriction ; but there are no dark masses at all corre- 
sponding to those of the posterior vesicular columns. In receding from the dorsal region, 
both upwards and downwards, the posterior cornua gradually separate, and the anterior 
cornua become enlarged. In Mammalia, and especially in Man, it has been seen that, 
through the middle of the cervical and lumbar enlargements, the cells on the inner side 
of the cerrix cornu are reduced in size. In Birds, on the contrary, they are much 
larger than in any other region. This is particularly the case in the lumbar enlarge- 
ment, especially near its middle, where they form a distinct group, which is traversed 
and surrounded by the posterior roots of the nerves (see M, figs. 34, 35, and 36, 
Plate XXIII.). They are mostly oval and round, with large nuclei, and send out 
their processes in difierent directions. In the corresponding part of the cervical region 
the larger cells are less numerous, but are mingled with others of a smaller kind. 
In Pep tiles, it is only in the conus medullaris that the posterior cornua are united into 
a single mass. In a transverse section they present no dark masses resembling those of 
the posterior vesicular columns, but only a few cells, of various shapes, at their bases. 
A distinct stratum, however, of small fusiform cells, in connexion 'with the fibres of 
the posterior roots of the nerves, extends diagonally from the point of each cornu to 
the posterior commissm-e, which is also interspersed with numerous nuclei, like those 
of the epithelium which lines the canal. In the cervical and lumbar enlargement, the 
cells, as well as the stratum which they form, are larger than in the dorsal region. 
(See figs. 44 & 45, Plate XXV.). 
On the Grey Substance of the Filum Terminate. 
In the conus medullaris of the human cord, as soon as the posterior cornua have 
united at their inner sides in a .single mass (fig. 19, Plate XXIII.), the gelatinous sub- 
stance {g') becomes continuous from side to side in a curve with its concavity backwards, 
in which the posterior columns (A) are included *; but, as it descends through the f him 
The continuity of the gelatinous substance across tlie middle line was asserted in my first communica- 
tion, and has since been found in birds by Metzlee, ‘De Medullae spinalis Avium Textura,’ p. 14 (1855). 
Stilling, however, in his late work, denies the fact, and maintains “ that the middle portion is ffrei/, and not 
f/elatmous^suhstance (“das Mittelstiick ist graue Substanz, und nicht gelatinose ”) ; and adds that my 
method m preparation rendered these two substances too transparent to perceive any difference between 
MDCCCLIX. o „ 
