THE CRANIAL NERVES. 87 
of the back, and then runs backwards and downwards 
round the side wall of the pharynx, running along the 
hinder border of the fourth division of the petrohyoid 
muscle: behind this muscle it divides into its main 
branches. 
i. The ramus laryngeus: loops round the posterior 
cornu of the hyoid and round the pulmocutaneous 
artery close to its origin from the aortic trunk : 
passes inwards dorsad of the artery to the middle 
line where it ends in the larynx. 
ii, The ramus cardiacus: passes dorsad of the pul- 
monary artery to the interauricular septum of 
the heart, and to the sinus venosus. 
iii, The rami pulmonales: follow the course of the 
pulmonary artery to the lung, in which they end. 
iv. The rami gastrici: usually two in number: run 
through the partial diaphragm formed by the 
anterior fibres of the obliquus internus muscle, 
and end in the walls of the stomach. 
The dorsal portions of the several branches of the vagus are best 
dissected from the side: to see them properly, the shoulder girdle 
and fore-limb must be removed and the esophagus well distended - 
the terminal branches must be dissected from the ventral surface. 
IV, The Cranial Portion of the Sympathetic Nervous 
System. 
The main sympathetic trunk of each side extends forwards in 
front of the first ganglion, and enters the skull at the foramen 
in the exoccipital bone through which the glossopharyngeal 
and vagus nerves pass out: it is connected with the vagus 
nerve, and then runs forwards within the skull to the Gasserian 
ganglion of the trigeminal nerve, in which it ends. 
C. Histology of Nerves. 
Nervous matter consists histologically of elements of two 
kinds, nerve cells and nerve fibres. The nerve cells are 
branching nucleated cells connected by their processes with one 
another and with the nerve fibres. The nerve cells are the 
