DISSECTING MANUAL. 



Inferior petrosal : Each runs from the cavernous sinus along the 

 lower border of the petrous bone and margin of the basilar part 

 of the occipital, to join the internal jugular in the jugular fora- 

 men. Spheno-parietal: Each lies on the under surf ace of the small 

 wing of the sphenoid and ends in the cavernous sinus. [886] 



Cranial Veins. The diploic veins drain the diploe and usu- 

 ally join a sinus. The vence comites accompany their arteries 

 and usually join a sinus. The vence Galeni are two lateral 

 veins which run between the layers of the velum interpositum 

 from apex to base and join (vena magna) to end in the straight 

 sinus. Emissary veins communicate with the exterior of the 

 cranium, viz.: from the superior longitudinal sinus through 

 the foramen caecum and parietal foramina; from the lateral 

 sinus through the mastoid and posterior condylar foramina; 

 and from the cavernous sinus through the carotid canal and 

 foramen ovale (or Vesalii), and through the ophthalmic vein 

 to the angular vein. [880] 



THE SPINAL CORD. 



Spinal Cord. This is cylindrical, slightly flattened in front 

 and behind, and lies in the spinal canal. Beginning at the fo- 

 ramen magnum, where it is continuous with the medulla, it 

 extends to the body of the first (lower border) or second (up- 

 per border) lumbar vertebra; there it forms a tapered end 

 (conus medullaris) which is prolonged by a narrow thread (filum 

 terminale) attached to the back of the coccyx. Its girth is 

 uniform in most of the dorsal region, but is gradually increased 

 between (cervical enlargement) the upper end of the cord and 

 the second dorsal vertebra, being most marked at the fifth or 

 sixth cervical vertebra; it also increases (lumbar enlargement) 

 below the tenth dorsal vertebra, being most marked at the 

 twelfth and then tapering rapidly. Three membranes sur- 

 round it. The pia mater, the most internal, is fibrous, invests 

 it closely and sends septa into it. The arachnoid, next exter- 

 nally, is delicate and separated from the pia by the subarach- 



[50] 



