966 THE OSTEOLOGY AND MYOLOGY OF THE DEATH ADDER, 



The Spinal Nerves. 



The spinal nerves emerge from the foramen formed by the 

 notches at the bases of adjacent laminae. They divide in the 

 usual manner into anterior and posterior primary divisions. 



The posterior primary division runs outwards for a short distance, 

 and divides into an external and internal branch. 



The external branch runs backwards and upwards, winding 

 round the pedicle of bone supporting the prezygapophysis, betweeA, 

 therefore, the superior facet of the transverse process, and the 

 tubercle of bone above. Passing under the origin of the levatores 

 costarum externi, it ascends and pierces the fibres of the rotatores 

 dorsi, which lie between the zygapophyses ; supplying these muscles, 

 it then comes to lie between the semispinalis and the multifidus, 

 to each of which it gives a branch, and ultimately is lost in the 

 spinalis dorsi. 



The external branch runs upwards and outwards, and, winding 

 round the internal side of a levator costse externus, it comes to lie on 

 this muscle, and beneath the longissimus to which it gives a branch. 

 After this it pierces through the aponeurosis formed by the 

 tendons of insertion of the longissimus, and breaking up into 

 branches is lost in the sacro-lumbalis column. 



The anterior primary division is a larger trunk than the poste- 

 rior. It runs outwards between a levator costss internus above, 

 and the subvertebral rectus below (internal), thus separating the 

 internal oblique stratum from the transverse. Soon it gives off 

 two branches, one going to each levator costae externus, the other 

 to a levator internus. 



The main branch runs outwards between the external inter- 

 costals and the depressores costarum. It gives off a well marked 

 branch which supplies the depressores costarum, and a little more 

 externally it supplies the transversalis muscle with a large twig 

 which runs between the retrahentes costarum and the transver- 

 salis. When the main trunk reaches the point where the depres- 

 sores are inserted it divides into two divisions. The larger of 



