THE FROG 109 



into two nerves,— the maxillary and the mandibular,— the former 

 of which passes along the mediocentral wall of the orbit to the 

 upper jaw, the latter along the laterodorsal wall of the orbit to 

 the lower jaw. 



The palatine is the hindermost of the nerves leaving the Gas- 

 serian ganglion. It runs along the ventral wall of the orbit and 

 innervates the mucous membrane of the mouth, with which it 

 lies in contact. The hyomandibular runs laterally from the gan- 

 glion to the angle of the mouth. 



The ninth and tenth cranial nerves— the glossopharyngeal and 

 the vagus, or pneumogastric, respectively— arise from the side of 

 the medulla, back of the auditory nerve, by four roots. These 

 uniting form a single nerve, which emerges from the cranial cavity 

 by a foramen at the side of the foramen magnum. Immediately 

 back of this foramen it expands into the large jugal ganglion, 

 from which the glossopharyngeal and the vagus proceed. The for- 

 mer passes forward to the tongue; the latter passes backward 

 along the pharyngeal wall, giving off branches which supply the 

 muscles of the shoulder, the larynx, the heart, the lungs, and 

 the stomach. 



Exercise 14. Draw the lateral aspect of the brain on a scale of 3, and 

 the cranial nerves so far as observed. 



Study the ventral surface of the brain. Cut the cranial nerves 

 and remove the brain from the skull. Put it in a dish of water 

 and study its ventral surface. Identify the olfactory lobe, the 

 hemispheres, and the structures belonging to the diencephalon. 

 The optic nerves will be seen issuing from the optic chiasma, a 

 structure formed by the crossing of the optic nerves on the ventral 

 side of the brain. Behind the optic chiasma is the infundibulum, 

 a large median projection which is divided into a right and a left 

 lobe, from the hinder end of which extends a flattened body 

 called the pituitary body or hypophysis. This body is lodged in 

 a depression in the floor of the cranial cavity, and usually remains 

 there after the brain is removed from the skull. 



The ventral portion of the midbrain is formed by the crura 

 cerebri, which lie beneath the optic lobes and are partly concealed 



