236 SUMMARY. 



similar muscles and contributes to the ciliary nerves, which are not so numerous as in 

 man, and do not always proceed from a ganglion. The fourth arises behind the optic 

 lobes in the four superior classes, and has the same destination in the superior oblique 

 muscle ; in man, it communicates with the lachrymal nerve. The fifth arises prin- 

 cipally from the oblong medulla in the four superior classes, half of the larger portion 

 in man, mammalia, and birds arises from a similar involuntary centre, the other half 

 from the sensitive centre in the floor of the fourth ventricle. The smaller portion in 

 man arises from the oblique tract of the annular tubercle, and in mammalia from the 

 trapezoid body ; it is not so distinct in the other classes. Some interchange similar to 

 that in the Gasserian ganglion exists in all. There are always three trunks, but in 

 some fishes more. The first trunk supplies the parts about the orbit and fore-head, 

 the superior nasal extends through the nose to the skin near the anterior part of this 

 organ in mammalia, and in birds and amphibia to the anterior portion of the palate 

 and beak. The second trunk gives branches to the temple and horn, the inferior part 

 of the orbit, the nose, the palate, and teeth ; its principal portion terminates in the 

 upper lip or the part answering to this, and is usually larger for making the snout an 

 instrument of feeling when the nerves of the toes are less. The third trunk supplies 

 the skin on the anterior surface of the external ear, and part of the temple and face 

 in mammalia ; the inferior dental supplies the teeth and bone of the lower jaw, and 

 the part corresponding with the lower lip in the four superior classes ; the mylo- 

 hyoideal nerve in some of mammalia sends a branch into the face to communicate 

 with the hard portion ; it is very small in the goose and very large in the pelican : in 

 the turtle there are two branches, and in the snake three ; the other branches of this 

 trunk vary, according to the presence or absence of muscles and other parts, or the 

 necessity for modified functions. The gustatory, as a large nerve for the sense of 

 taste, exists only in mammalia, a branch analogous to one given by it to the lining 

 membrane of the mouth may be resembled by those of the inferior dental in the other 

 classes. In some fishes the fifth gives off the auditory nerve, and furnishes a large 

 posterior branch for communicating with the spinal nerves, especially those of fishes. 

 The sixth exists in the four superior classes with very little difference except in size, 



