438 im. J. L. CLAEKE OX THE GEET SEBSTAXCE OE THE SPIXAL COED. 
into two parts, namely, the cornu and the cervix cornu*. The ca^ut consists of 
the broad or expanded extremity of the cornu, and is separated from the cervix by an 
imaginary line drawn across from the opposite anterior extremities of the arched lamina 
of gelatinous substance. In some regions of the cord a line of somewhat paler substance 
partially marks the separation. The cervix comprehends the remaining portion of the 
cornu as far forwards as the level of the central canal. This distinction is grounded 
on the facts, — 1, that in ascending the medulla oblongata, the part which I designate the 
caput cornu is thrown aside from the rest, as a distinct mass which is traversed in 
succession by the vagus and glossopharyngeal nerves, and then becomes the principal 
nucleus of the sensory root of the trifacial ; and 2, that, independently of the gelatinous 
substance which surrounds it, it differs in structure from the cervix, or remaining part of 
the cornu, which, in the medulla oblongata, supplies the grey substance of the posterior 
pyramid and restiform body\. This distinction is not only consistent with anatomical 
facts, but will be the means, I think, of adding clearness and precision to the description 
of these parts. 
The caput cornu posterioris varies in form in different regions of the cord. In the 
upper part of the cervical region it is long and pointed, or pyramidal ; broader and more 
rounded in the lumbar enlargement and in the conus medullaris ; and again pointed, 
or somewhat pyramidal, through the whole of the dorsal region in Man (see fig. 12. 
Plate XXV.; fig. 15, Plate XXI.; fig. 17, Plate XXIII. ; figs. 5 & 6, Plate XXI.). 
From its border a network of blood-vessels, accompanied by nerve-fibres, extends outwards 
through the posterior and lateral columns (see fig. 1, Plate XIX.), and in the lumbar 
region especially is very conspicuous around its pointed extremity, at the bottom of the 
lateral fissure, where it divides the white columns into a number of separate fasciculi of 
different shapes and sizes. 
posterior coruu, — an opinion which is perhaps founded on the statement of Eolaiodo, that it forms tlie 
posterior third of the grey crescent. 
* In my memoir on the Medulla Oblongata I have written “ caput coruws posterioris.” As I have heai’d 
that this has been objected to by an “eminent classic,” on the ground that the norm cornu is indeclinable 
in the singular number, I may here take the opportunity of informing any one who has made or may make 
a similar objection, that the expression is perfectly grammatical and correct ; for there is another and more 
ancient form of the same noun, which makes both the nominative and genitive singular to end in Tliis 
ancient form may be found in several of the Latin classics — in Celsus, Cicero, Lucan, and the elder Pliny. 
In Pliny it occurs frequently : see Historia Naturalis, lib. viii. 29 ; lib. x. 90 ; lib. xiii. 51 and 52 ; lib. xxviii. 
42, 46, and 64. I find that it has also been used by Metzler in his dissertation Z>e medulias spinalis avium 
textura. Dorpat, 1855. I employed it on account of the distinctive character of its genitive ; but as it appears 
necessary at times to use the words cornu and cornua, because they are so geuerally luiown, I shall confine 
myself to the more modern form of the noun. 
t See the author’s “Medulla Oblongata,” Philosophical Transactions, Part I. 1858, figs. 12, 15, 16, 19. 
and 23. The grey tubercle of Eolando, which reaches the surface on each side of the medulla ohlonqala, is 
generally considered to consist of the gelatinous substance, but in fact it includes the whole dilated extremity 
of the posterior comu, or caput cornu. 
