THE SPINAL CORD 765 
the second thoracic. 
mm.) and its dorso-ventral nearly half an inch (ca. 12 mm.). 
Its maximum transverse diameter is about an inch (ca. 25 
The lumbar enlarge- 
ment (Intumescentia lumbalis) is situated in the fourth and fifth lumbar vertebre. 
70 
IY th 8 9 
11 
12 
6 
Fic. 626.—VeENTRAL View oF MepuLia OBLONGATA 
AnD First anpD Seconp SEGMENTS OF SPINAL 
Corp oF HorsE; THE MEMBRANES ARE CUT AND 
REFLECTED. 
1, Lig. suspensorium arachnoideale; 2, right cere- 
brospinal artery; 3, 5, digitations of lig. denticulatum; 
4, free border of lig. denticulatum; 6, middle spinal 
artery; 7, basilar artery; 8, pons; 9, arachnoidea; 
10, dura mater; 11, 12, ventral root-bundles of first 
and second segments of spinal cord; VJ, N. abducens; 
TX, X, glosso-pharyngeus and vagus; XJ, accessory, 
medullary part; XJ’, accessory, spinal part; a, line 
between medulla oblongata and spinal cord. (Dexler, 
in Ellenberger-Baum, Anat. d. Haustiere.) 
It is a little narrower than the cervi- 
cal enlargement, and its dorso-ventral 
diameter is also slightly smaller. Be- 
hind this the cord tapers rapidly to 
form the conus medullaris. The tip 
of the latter is continued by a delicate 
glistening strand, the filum terminale, 
which is composed largely of fibrous 
tissue continued from the pia mater, 
covered by arachnoid. 
Fic. 627.—Caupa Equrna. 
1, Dura and arachnoidea divided and reflected; 2, 
spinal cord; 3, nerve-roots. (From Leisering’s Atlas, re- 
duced.) 
The surface of the spinal cord is 
divided into two similar halves by a 
dorsal median groove and a ventral 
median fissure. On either side of the 
former is the dorso-lateral groove (Sul- 
cus dorsalis lateralis), at which the fibers 
of the dorsal nerve-roots enter the cord; 
it is faint except at the enlargements, and is represented by two grooves in the first 
cervical segment. 
The ventral root-fibers as they emerge from the cord do not 
form a continuous series, but arise from a zone (Area radicularis ventralis) 3 to 5 
