5,'U TIIK (MiANIAI, NKKVES. 



of the fifth pair, and :uv tin- only muscular functions directly interfered 

 with liy this operation. There is a diHerenec, ho\\ ever, in Mir ultimate 

 consequences uhich follow |>:i ralysis of mast icat ion, according to the 

 species of animal alfcctcd. If the fifth pair, or its inferior maxillary 

 division, \\civ destroyed on both sides in either u carnivorous or 

 herbivorous animal, death would follow from inanition, owing to the 

 impossibility of preparing the food for deglutition. If the injury were 

 inllictcd upon one side only, it, would be equally fatal in the hcrbivora, 

 by preventing the alternate lateral movements of the jaw; while in a 

 carnivorous animal the vertical movements, which are more import-nut, 

 would be less seriously alleetcd, since they might still be performed, 

 though imperfectly, by the muscles of the opposite side. 



I'.iit the most peculiar secondary result, of paralysis of the muscles of 

 mastication on one side is seen in the rodcntia. In these animals the 

 most important teeth are the four incisors, two in the upper and two in 

 Mir lower jaw, which are used for gnawing through hard substances, and 

 which grow continuously from the tooth pulp below, thus supplying the 

 waste caused by wearing away their edges. The tooth move against 

 each other in an exact vertical plane, the upper and lower incisors on 

 each side meeting e:ich other, and thus by mutual attrition keeping their 

 chisel like edges at a con espoiiding level. If the fifth nerve be divided 

 in I hese animals, the lower jaw becomes deviated toward the operated 

 side in consequence of the paralysis of the corresponding petrygoid 

 muscles. The edges of the four incisor teeth then no longer correspond 

 with each other, but are so shifted that one of those in the upper and 

 one in the lower jaw do not meet \\ith any opposing edge, and are con- 

 sequently no longer worn away. According to the experiments of Ber- 

 nard on rabbits, (he line of junction between the edges of t he teeth, 

 instead of being hori/.ontal, then becomes oblique, being directed from 

 abo\e downward, from the operated toward the sound side, and the 

 same fact has been observed by Hint. 1 If the animal survive for a 

 considerable time, tin- teeth which are no longer worn away, as they 

 continue to grow from the tooth-pulp below, may become excessively 

 elongated. \\'e have seen an instance in the woodchuck ( A ret omys 

 monax) of lateral deviation of the teeth from a reunited fracture of the 

 lower jaw, in which the upper incisor on one side and the lower on the 

 other had increased to live or six times their natural length, and had 

 probably caused the death of the animal by penetrating the soft pails 

 about, the head and interfering with the movement of the jaws. 



Antixtainoh'c lirtuicln-K <>/' fhc /'//'// /'rt/>. Although the separate 

 regions of the face are supplied in a general way by the three great 

 divisions of this nerve, there is yet more or less communicat ion between 

 them by intermingled filaments from (litl'erent sources, and the separate 

 branches of each division communicate with considerable frequency. 

 Thus the infra-orbital nerve, which sends filaments to the lower eyelid, 



1 Physiology of Man ; Nervous Svstem. Now York. 1872, p. 198. 



