THE SPINAL NERVES. 175 



f. The Ramus laryngeus [Becurrens vagi), (Figs. 114 and 115 

 X'^l) runs for some distance parallel to the pneimiogastric, separated 

 from it by the jjetrohi/oideus 17 ; arriving at the hinder cornu of 

 the hyoid bone the nerve loops roimd the Arteria 2oulmo7ialis, and 

 divides into two branches for the supply of the larynx. 



g. The Uami gastnci (Fig. 114 A'3/7) are usually two in number: 

 they pierce the partial diaphragm formed by the anterior fibres of 

 the M. obliciuus hit emus and terminate in the walls of the stomach, 



h. The Band pnlmonales (Figs. [ 14 and 115 A3/;) also perforate 

 the partial diaphragm, and then course along the pulmonary arteries 

 to the lungs. 



i. The Bamus canliacus (Figs. 114 and 115 Xy). This nerve 

 is usually smaller on the right side than on the left ; it passes 

 along the dorsal svu'face of the pulmonary artery and Vena cava 

 svjper'wr to the Sinus venosns ; in this course it gives off two or three 

 twigs to the roots of the lungs : the two nerves communicate just 

 before reaching the heart and pass on to the auricular septum, 

 whence they are distribvited to the heart. 



j. A slender Laryngeal nerve arises from the vagus along*side 

 the Bamus canliacus ; it courses along the hinder end of the greater 

 cornu of the hyoid to the outer side of the pharynx, which it 

 pierces to pass to the larynx. 



F. The Spinal Nerves. 



I. General description. Ten pairs of nerves arise, as already 

 described (p. 135), from the spinal cord; each nerve has two 

 roots, a ventral or anterior, and a dorsal or posterior, which unite 

 at their points of exit from the intervertebral foramen : just 

 before, and for a short distance beyond this union, each dorsal 

 root bears a ganglionic enlargement. 



1. The length and direction of the various Nerve-roots vary 

 greatly; the roots of the anterior spinal nerves run a very short 

 course, almost transversely outwards, from their points of origin to 

 the intervertebral foramina : the roots of the middle and posterior 

 nerves, in consequence of the vertebral column being considerably 

 longer than that part of the cord belonging to it, pass obliquely 

 backwards to the foramina, the hinder nerves of the Cauda equina 

 running for a considerable distance in the vertebral canal (Fig. 116). 

 The relations of these roots are as follows : — 



