268 



FIFTH PAIR OF NERVES. 



supply. Deriving its origin from the same 

 source, and anastomosing freely with both in 

 all parts of their respective courses, it is pre- 

 pared to take the place of either, one might say, 

 at a moment's warning, and the freedom of 

 this communication affords a sufficient indica- 

 tion to surgeons how ineffectual in cases of 

 wounds a single ligature would be ; in short, 

 here as in other places where arterial communi- 

 cations are so free, the rule of practice is so 

 clearly pointed out by the anatomy as almost 

 to render it superfluous to appeal to experience. 

 The relations of this artery to operations being 

 very similar to those of the posterior tibial, we 

 refer on this head to the article TIBIAL AR- 



TERIES. 



(R. B. Todd.) 



FIFTH PAIR OF NERVES. This title 

 is derived from the relation which the nerve 

 bears numerically to the other encephalic pairs; 

 it is the fifth nerve met with on the base of the 

 brain counting from before backwards. The 

 fifth is also called the trigeminal (Winslow) 

 and the trifacial (Chaussier) nerve. It is the 

 nerve upon which the general and tactile sensi- 

 bility of the face and its cavities, as well as the 

 voluntary power of certain muscles of these 

 parts, depends. 



The following account of this nerve is meant 

 to apply especially to the human subject; but 

 as a knowledge of its structure and distribution 

 in other animals must contribute very much to 

 enlighten us in regard to its true character and 

 properties in man, occasion has been taken to 

 mention those particulars by which it is dis- 

 tinguished throughout the animal series. 



The fifth nerve is connected at its one ex- 

 tremity with the medulla oblongata, whilst 

 its other end is distributed to the eye and its 

 appendages, to the nostrils, to the palate, the 

 mouth and tongue, to the salivary glands, to 

 the ear, to the integuments and muscles of 

 the face, forehead, and temple, and to the 

 muscles which move the lower jaw in mas- 

 tication, the temporal, pterygoid, and mas- 

 seter muscles. The general distribution of the 

 nerve throughout the animal series corres- 

 ponds to that in man ; but, in certain animals 

 and classes, varieties are presented, which 

 claim our attention equally, whether as matters 

 of curiosity or of physiological interest. In 

 some individuals of the class Mammalia, the 

 eyes possess a very inferior degree of develop- 

 ment; a distinct optic nerve either does not 

 exist or its existence is a matter of doubt, 

 and its place is supplied, in part or alto- 

 gether, by a branch of the second division 

 of the fifth nerve: thus, in the Mole, accord- 

 ing to M. Serres,* the optic is altogether 

 absent, and its place is supplied by a branch 

 of the fifth ; but, according to Treviranus,f 

 that animal is provided with an optic nerve, 

 as large as a human hair, and according to 

 CarusJ it joins an optic branch from the fifth, 

 and the two concur to form the retina. In 



* Anatomie Comparee du Cerveau, &c. 

 t Journal Complemeritaire. 

 J Journal Compl. 



other animals of the same class the optic seems 

 decidedly absent, and its place is supplied al- 

 together by the fifth. Among Reptiles also in- 

 stances occur, in which the optic nerve is 

 wanting. According to botji Treviranus* and 

 Serres, f the fifth nerve takes the place of 

 the optic in the Proteus Anguinus. A va- 

 riety in distribution, still more remarkable, 

 is presented in the disposition of the fifth 

 nerve in Fishes. Among the Rays the audi- 

 tory appears to be, not a distinct nerve, but 

 a branch of the fifth : J the special organs, 

 with which they are provided, likewise, in 

 many instances, derive their nerves from the 

 fifth pair; thus, in some the electrical organs 

 are supplied by that nerve, and also the albu- 

 mino-gelatinous organs: lastly, in many the 

 nerve is distributed || in a manner and to an 

 extent for which there is no analogy among 

 other animals, the fins being throughout fur- 

 nished with branches from the fifth. Hence 

 in Fish, in which the distribution of the 

 nerve is so much more extended than in 

 other animals, both the size of it is propor- 

 tionally greater, and it consists of a greaterlf 

 number of divisions ; these, which in the three 

 other classes of vertebrate animals are only 

 three, amounting with them to from three to 

 six. See sketch of nerves in the Ray and Cod. 

 (Figs. 144, 145.) 



The size of the fifth nerve is very great, it 

 being by far the largest of those proceeding from 

 the medulla oblongata. In this respect it pre- 

 sents much variety according to the animal or its 

 class. M. Serres states that, the nerves being 

 proportioned always to the volume of the 

 organs from whence they proceed, the extent 

 of the face and of the organs of the senses 

 taken together gives the size of this nerve in 

 the different classes of vertebrate animals. 

 Among the Mammalia the extent of the face 

 and of the organs of the senses increases pro- 

 gressively from Man to Apes, the Carnivora, 

 the Ruminantia, and the Rodentia, and, ac- 

 cording to him, the size of the fifth nerves 

 follows in a general manner the same pro- 

 gression. Birds are remarkable for the atrophy 

 of the muscles of the face and of several of 

 the organs of the senses, and their fifth nerve 

 is far from presenting the developement to be 

 observed in the inferior Mammalia. Reptiles 

 are still lower than Birds with regard to the 

 dimensions of the nerves of the fifth pair; 

 while in Fish** the size of the nerve is very 

 great, and even surpasses in some the volume 

 it presents in the other classes.ft However just 

 the estimate of the comparative volume of the 

 nerve in different animals, as here stated, may 



* Op. cit. 



t Op. cit. 



j Desmoulins, Journal de Physiologic, t. ii. 

 Serres, op. cit. 



Desmoulins, Anatomie des Systemes Nerveux, 

 &c. Carus, Rudolplii. 



|| riesmoulins, op. cit. 



l" Desmoulins, op. cit. 



** See Sketches of Nerve in the Ray and Cod, 

 figs. 144, 145. 



tt Serres, Anatomic Comparee du Cerveau, 

 dans les quatre classes dcs Animaux Vertebres. 



