216 



SEGMENTATION OF THE HEAD. 



first) stands in a definite relation to the nerve and artery of the 

 arch in which it is situated. 



The comparative results of these three independent methods 

 of determining the segmentation of the head are in the sub- 

 joined table represented in a form in which they can be 

 compared : — • 



Table of the Cephalic Segments as determined hy the Nerves, Visceral 

 Arches, and Head-Carities. 



In the above table the first column denotes the segments of 

 the head as indicated by a comparison of the three sets of organs 

 employed. The second column denotes the segments as ob- 

 tained by an examination of the nerves ; the third column is for 

 the visceral arches (which lead to the same results as, but are more 

 convenient for our table than, the visceral clefts), and the fourth 

 column is for the head-cavities. It may be noticed that from 

 the second segment backwards the three sets of organs lead to 

 the same results. The head-cavities indicate one segment in 

 front of the mouth, and now that the ophthalmic branch of the 

 fifth has been dethroned from its position as a separate nerve, 

 the eye-nerves, or one of them, may probably be regarded as 

 belonging to this segment. If the suggestion made above 

 (p. 208), that the walls of the first cavity become the eye-muscles, 

 be correct, the eye-nerves would perhaps after all be the most 

 suitable nerves to regard as belonging to the segment of the first 

 liead-cavity. 



