DISSECTION OF THE BACK AND THORAX. 



141 



foramen in the neck a branch of the vertebral artery enters the spinal 

 canal. In the back similar branches enter from the dorso-spinal division 

 of the intercostal arteries, in the loins the branches emanate from the 

 Inmbar arteries, and in the sacral region from the lateral sacral artery. 

 As a rule, the branches entering by adjacent foramina anastomose, and 

 then give off branches to the cord and the vertebral bodies. 



The Veins of the Spinal Cord are tortuous, and form on its surface 

 a plexus from which the blood passes into two large veins that lie one at 

 each side of the superior common ligament. These receive also veins 

 from the vertebral bodies, and they are drained by vessels that issue by 

 the intervertebral foramina to join the vertebral, intercostal, lumbar, or 

 lateral sacral veins. 



Directions. — For the examination of the structure of the spinal cord, 

 a few inches of it with the roots of the nerves intact should be procured, 

 and kept in spirit or some other hardening fluid for at least a week. 

 A portion from the spinal cord of any of the domestic animals will serve 

 the purpose ; but, from its larger size, that of the horse is to be pre- 

 ferred. 



■ Stbuctube of the Spinal Cord. The meninges having been removed, 



the student will note the following points regarding the surface of the 



cord : — It approaches the 



cylindrical m lorm, but is ' ■? 



slightly flattened above and 



below. It is traversed in 



the longitudinal direction 



by three fissures, and a 



fourth is sometimes de 



scribed. The superior med 



ian fissure is a narrow 



interval extending into the 



cord along the middle line 



of its upper face. It is 



occupied by neuroglia. The 



inferior median fissure is an 



actual cleft penetrating the 



cord along the middle line 



of its lower face. It is 



occupied by a process of 



pia mater. The supero- 

 lateral fissure is a faint 



surface depression extend- 

 ing on the side of the cord, 



along the line of emergence 



of the superior roots of the spinal nerves, 



Fig. 17. 



Teausveese Section of Spinal Cokd of Calf (Klein). 



1 Superior median fissure ; 2. Central canal, in grey 

 (superior) commissure ; 3. Superior horn of grey matter ; i. 

 Inferior horn of grey matter ; 6. Process of pia mater m 

 inferior median fissure ; 6. White (inferior) commissure ; 

 7 Inferior column of white matter ; 8. Inferior nerve roots ; 

 g' Lateral column of white matter; 10. Pia mater; 11. 

 Superior column of white matter ; 12. Superior nerve roots. 



The infero-lateral fissure has 



