THE SPINAL CORD 



649 



■vontral dianictcr is also sli<i;htly smaller. Behind this the cord tapers rapidly to 

 form the conus medullaris. The tip of the latter is continued by a delicate glisten- 

 ing strand, the filum terminale, which is composed largely of fibrous tissue con- 

 tinued from the pia mater, covered by 

 arachnoid. 



Th(^ surface of the spinal cord is 

 divided into two similar halves ])y a 

 dorsal median groove (Sulcus medianus 

 dorsalis) and a ventral median fissure 

 (Fissura mediana ventralis). On either 

 side of the former is the dorso-lateral 



Fig. 495. — Ventr.\l View of Medulla Oblongata 

 AND First -\nd Second Segments of Spin.\l 

 Cord of Horse; the Membranes are Cut 

 AND Reflected. 



/, Lig. suspensorium arachnoideale; 2, right 

 cerebrospinal artery, S, 5, digitations of lig. denticu- 

 latum; 4, free border of lig. denticulatum; 6, middle 

 spinal artery; 7, basilar artery; ti, pons; 9, arach- 

 noidea; 10, dura mater; //, 12, ventral root-bundles 

 of first and second segments of spinal cord; VI., N. 

 abducens; IX, X, glo.sso-pharyngeus and vagus; XI, 

 accessory, medullary part; XI', acce.ssory, spinal part; 

 a, line between medulla oblongata and spinal cord. 

 (De.xler, in Ellenberger-Baum, .Vn.it. d. Haustiere.) 



groove 



which 



(Sulcus dorsalis lateralis) at 

 the fibers of the dorsal nerve- 



illlW 



Fir,. 496. — Cauda Equina. 

 1, Dura and arachnoidea divided and reflected; 

 2, spinal cord; ,:J, nerve-roots. (From Leisering';- 

 reduced.) 



Atlas 



a 



little 



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 ven- 

 lateral to the ventral median fissure, 



tralis) 3 to 5 mm. in width 

 and no groove is found here. In the greater part of the cervical region and 

 the anterior part of the thoracic region there is a shallow dorsal paramedian 

 groove (Sulcus intermedins dorsalis) a short distance lateral to the median 



