THE CRANIAL OB ENCEPHALIC NERVES. 703 



however this may be, this plate, which was discovered by Eouget, at first in 

 reptiles, then in birds and mammals, has been studied by several micro- 

 graphs, who are agreed as to its existence. There can, therefore, be no 

 .doubt that it is the ultimate termination of the motor-nerves. 



The mode of termination of the sensitive nerves varies as they are 

 sensorial or general sensibility nerves. It appears to be demonstrated that the 

 tubes of the sensorial nerves have at their extremity an elongated cell, 

 analogous to that from which they started. An idea has been given of 

 this arrangement in describing the olfactive portion of the pituitary mucous 

 membrane. 



The other sensitive nerves have been supposed to terminate by peripheral 

 loops, and again by free extremities passing into kind of cell elements. It 

 is certain that these two modes exist simultaneously ; recurrent sensibility, 

 which Claude Bernard demonstrated in some cranial nerves, proves 

 that certain nerves terminate by loops. Our own experiments have 

 shown : 1 , That this recurrent sensibility is a general phenomenon belonging 

 to the sensitive nerves of the limbs, and even to all the sensitive ramifications 

 of the spinal nerves ; 2, That the recurrent anastomotic loops are formed at 

 different parts along the course of the nerves, either beneath the integument 

 or in its texture. It is, then, proved that the peripheral loops constitute a 

 mode of termination of the sensitive nerves. But this is not the only mode 

 of termination observed. In the papills of the skin, in certain regions- 

 hand, foot, lips, tongue, glands, clitoris — the cmyusdes of Meissner, or tactile 

 corpuscles, are found ; these are composed of condensed connective tissue, 

 and are conical, like a pine-cone, the summit towards the periphery. By their 

 base enters one or more nerve-tubes, that ascend toward the apex in 

 a spiral manner. In the conjunctiva, lips, etc., are also found rounded bodies 

 analogous in their structure to the tact corpuscles, and which are named the 

 corpuscles of Krause. Lastly, on the course of the collateral nerves of the 

 fingers and in the mesentery of the Cat, are the Pacinian corpuscles : small 

 globular or ovoid bodies formed of several concentric layers of connective 

 tissue, and with a central canal into which penetrates and terminates, by one 

 or more enlargements, a filament from the nerve-trunk (reduced to the axis- 

 cylinder only).' 



CHAPTER I. 



THE CEANIAL OR ENCEPHALIC NERVES. 



The cranial nerves leave the encephalon in pairs, regularly disposed to 

 the right and left, and designated by the numerical epithets of first, second, 

 etc., counting from before backwards. 



Willis, taking for a basis the number of cranial openings through which 

 the nerves passed, divided them into nine pairs, with which he described 

 the first spinal pair, making it the tenth in the series of encephalic nerves. 

 This division being faulty in some respects, it was sought to perfect it. 

 HaUer commenced by removing the first spinal or suboccipital pair of 

 nerves to their proper region ; then followed Soemmering and Vicq-d'Azyr, 



' Arloing and Tripier. ' Kecherches sur la Sensibilite dos Teguments et des Nerfs 

 de la Main.' (Archives de Physiologie, 1869.) 



