380 DISSECTION OF THE SPINAL CORD. 



fibrous prolongation of the cord. The branches of this artery ramify in 

 the pia mater, some entering the median fissure. 



The posterior spinal arteries, one on each side, are continued from the 

 upper to the lower part of the cord, behind 

 Fig. 124. the roots of the nerves. These vessels are 



furnished from the same source as the ante- 

 rior, and their continuity is maintained by a 

 j., series of anostomotic branches, which enter 



the canal along the spinal nerves. Dividing 

 into small branches, the vessels of opposite 

 sides form a free anostomosis around the pos- 

 terior roots, and some offsets enter the poste- 

 rior fissure of the cord. 



The veins of the spinal cord are very tor- 

 tuous and form a plexus on the surface. At 



WilHiHK^ f intervals larger trunks arise, which accompany 



the spinal nerves to the intervertebral fora- 



MW/llBBllnk mina, and end in the veins outside the spinal 



canal. Near the top of the cord the veins are 

 united into two or more small branches ; after 

 1 I // iiill communicating with the intraspinal veins, 



JHfjIIHI UtV these join in the skull the inferior cerebellar 



raff/Hi IHTM - veins, or the inferior petrosal sinuses. 



^ ~O } '' //filllhyJ: d The SPINAL CORD (medulla spinalis) is the 



cylindrical elongated part of the cerebro- 

 spinal centre, which is inclosed within the 

 Illff/lll wm\^L. spinal canal. Invested by the membranes 



1V * before examined, the medulla occupies about 



two-thirds of the length of the vertebral canal, 

 and is much smaller than the bony case sur- 

 rounding it. 



The extent of the spinal cord is from the 

 upper border of the atlas to the lower border 

 of the first lumbar vertebra, but its termina- 

 tion inferiorly may be a little higher or lower 

 than that spot. In the embryo before the 

 third month the medulla reaches throughout 

 the spinal canal, but it gradually recedes as 

 the surrounding bones enlarge faster than it, 

 until it takes the position it has in the adult. 

 Its length is usually from fifteen to eighteen 

 inches. 



Superiorly the cord joins the medulla ob- 



' j| a longata ; and inferiorly it becomes pointed, 



being sometimes marked by one or two swell- 

 ings, and ends in the fibrous prolongation, 



MEMBRANES OP THE SPINAL CORD named the central ligament of the cord or 

 LAID OPBN, to show the lower filum terminale (fig. 124, d). 

 end of the cord with the filum The size of the spinal cord is much in- 

 terminaie. creased where the nerves of the limbs are 



. Dura mater, and 6, the fibrous attachec i. There are therefore two enlarge- 



baud fixing it to the coccyx. . i -, , i 



, ,., ments on it, viz., cervical and dorsal: the 



c. Pointed lower end of the cord. , 



d. Filum terminale of the cord. one in the neck reaches from the third cer- 



