THE CRANIAL OB E.\ CEPHALIC NERVES. 807 



the pituitary mucous membrane. Other examples will be given when studying 

 the organs of the senses. 



The other sensitive nerves — the cutaneous nerves, for example — ^have been 

 supposed to terminate by peripheral loops, and again by free extremities passing 

 into a kind of cell elements. It is certain that these two modes exist simul- 

 taneously ; recurrent sensibility, which Claude Bernard demonstrated in some 

 cranial nerves, proves that certain nerves have pre-ferminal pprip/tfral 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 and those of the face. 2. Tliat 

 the recuiTent anastomotic loops are formed at different parts along the course of 

 the nerves, either beneath the integuments or in their texture. It may be added 

 that there are found in the papilla of the skin, in certain regions — hand, foot, 

 lips, tongue, glands, clitoris — the corpuscles of Jleissner, or tactile corpuscles. 

 These ai'e composed of condensed connective tissue, and are conical, like a pine- 

 cone, the summit towards the periphery. By their base they enter one or more 

 nerve-tubes, which terminate in enlargements. 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, or corpuscles of Vater — small globular or ovoid bodies, formed of 

 several concentric layers of tissue, and with a central cavity or 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 Cranial or Encephalic Nerves. 



The cranial nerves leave the brain 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 cranial nerves. This 

 division being faulty in some respects, it was sought to perfect it. Haller com- 

 menced by removing the first spinal or suboccipital pair of nerves to their 

 proper region ; then followed Soemmering and Vicq-d'Azyr, who doubled the 

 seventh pair of Willis, and reduced his eighth into three distinct paii-s, according 

 to considerations derived from the destination and uses of these nerves. The 

 number of pairs of cranial nerves, their order of succession, and their nomen- 

 clature were then established in the following manner : — 



' Arloing and Tripier, " Renherches sur la Sensibility des Teguments et des Nerfs de la 

 Main" (Archivet de Phy$iologie. 1869). 



