NERVES. 



8T 



Fig. 17. 



ing tissue, or after forming a single narrow loop, as in the sensory 

 papillae, returns to the same or to an adjoining plexus, and pursues its 

 way to the nervous centre from which it set out. According to this 

 view, there is no more a termination of nerves, than there is of blood- 

 vessels. Both form circles. More recent observations seem, however, 

 to have demonstrated, that in different situations the loop-like appear- 

 ance is fallacious ; and that the ultimate fibres divide into fibrils, the 

 terminations of which are lost in the tissues. 



Investigations, again, by Henle and Kblliker 1 show, that some of 

 the peripheral nervous fibrils term- 

 inate in small bodies, seated espe- 

 cially in the nerves of the fingers 

 and toes, which, from their having 

 been discovered, in 1830, by Pacini 

 of Padua, have been called Pa- 

 cinian corpuscles; but of whose 

 uses little can be said. They have 

 not been observed on any motor 

 nerves, so that they would not seem 

 to have anything to do with motion. 

 They exist in many nerves of the 

 sympathetic class, and are not pre- 

 sent on many sensitive nerves ; so 

 that, it has been properly inferred, 

 they are probably not connected 

 with acuteness of sensation. 



Of the encephalic nerves, the 

 olfactory, auditory, and acoustic the Pacinian corpuscles . 



/ . i "L.'T B - Unusual form, from the mesentery of the cat; 

 nerves OI Special Sensibility showing two included in a common envelope: 



clearly pass on to their destination, a ' b are the two nen 

 without communicating with any other nerve. The spinal nerves, at 

 their exit from the intervertebral foramina, divide into two branches, 

 an anterior and a posterior, one being sent to each aspect of the body. 

 The anterior branches of the four superior cervical pairs form the cer- 

 vical plexus, from which all the nerves of the neck arise ; the last four 

 cervical pairs and the first dorsal form the brachial plexus, whence 

 proceed the nerves of the upper extremities ; whilst the branches of 

 the five lumbar nerves, and the five sacral form the lumbar and sciatic 

 plexuses; the former of which gives rise to the nerves distributed to 

 the parts within the pelvis ; the second to those of the lower limbs. 

 The anterior branches, moreover, at a little distance from the exit of 

 the nerve from the vertebral canal, communicate with an important and 

 unique portion of the nervous system, the great sympathetic. 



Each nerve consists of numerous fasciculi surrounded by areolar 



1 Ueber die Pacinischen Korperchen an den Nerven des Menschen und der Saugethiere, 

 Zurich, 1844; reviewed in Brit, arid For. Med. Rev., January, 1845, p. 78; and Todd and 

 Bowman, Physiological Anat. and Physiology of Man, i. 395, London, 1845, or Amer. edit.; 

 and W. Bowman, Cyclopaedia of Anat. and Physiol., by Dr. Todd, pt. xxvii. p. 876, Lond., 

 Mar., 1846. 



Pacinian Corpuscles. 

 A. Nerve from the finger, natural size ; showing 



