THE PIGEON 189 



the largest of the three, which enters the orbit and divides into 

 two branches, one supplying the temporal muscle and the other 

 running forward to the lower mandible. 



The sixth nerve, the abducens, is short and small. It arises on 

 the ventral surface of the medulla near the median line, nearly 

 opposite the base of the trigeminal nerve, and passes through the 

 floor of the skull to the orbit. It will be seen when the ventral 

 surface of the brain is studied. The seventh nerve, the facial, 

 arises just back of the trigeminal on the lateral side of the medulla, 

 and runs backward in two branches to the muscles at the base 

 of the head. The eighth nerve, the auditory, is larger than the 

 facial and arises immediately back of it. 



The ninth nerve, the glossopharyngeal, which arises on the side 

 of the medulla close to the auditory, and the tenth nerve, the 

 pneumogastric, or vagus, which arises close to the glossopharyn- 

 geal, pass out of the skull by the same foramen. Just outside 

 the foramen the glossopharyngeal merges into a large ganglion, 

 from which nerves are distributed to the muscles of the tongue and 

 the base of the skull. The pneumogastric nerve passes straight 

 back along the side of the neck to the body cavity, where it breaks 

 into branches which supply the trachea, lungs, heart, stomach, 

 and gizzard. 



The eleventh nerve, the spinal accessory,, is closely joined with 

 the vagus. It arises on the side of the spinal cord by a number 

 of roots, enters the cranial cavity through the foramen magnum, 

 and passes out again, together with the vagus and glossopha- 

 ryngeal, to the muscles of the neck. The twelfth cranial nerve, the 

 hypoglossal, arises near the medial line on the ventral surface of 

 the medulla; it leaves the skull by a foramen at its base and is 

 distributed to the muscles of the neck. 



Exercise 30. Draw a view of the lateral aspect of the brain and the 

 cranial nerves so far as they have been observed. 



Study the ventral surface of the brain. Remove the brain from 

 the head. Just behind the optic tracts is a median projection 

 of the diencephalon, the inf undibulum ; at its ventral end is the 

 pituitary body, or hypophysis, which is usually torn off when the 



