BY DR. BURDON-SA^ 7 DERSON. 255 



kind from those of direct excitation of the medulla, although 

 the augmentation of arterial pressure and other concomitant 

 phenomena are less considerable. In the case of the dorsalis 

 pedis, however, and other nerves to be immediately referred 

 to, there is a marked difference between the condition of the 

 arteries in the region to which the excited afferent nerve is 

 distributed, and those of the rest of the body. 



EXPERIMENTS SHOWING THAT THE SAME DEGREE OF EXCITATION 

 OF A SENSORY NERVE WHICH PRODUCES GENERAL CONTRACTION 

 OF THE ARTERIES IN OTHER PARTS OF THE BODY, DIMINISHES 

 THE TONUS OF THE ARTERIES OF THE PART TO WHICH THE Ex- 

 CITED NERVE is DISTRIBUTED. 



53. (1.) Excitation of the Nerves of the External 

 Ear of the Rabbit. The ear of the rabbit derives its sensi- 

 bility from two nerves, both of considerable size. One of 

 these, the posterior auricular, approaches the surface at the 

 back of the neck, very near the middle line, and runs forwards 

 and outwards, under a thin covering of muscle, to the root of 

 the ear, where it penetrates a process of cartilage, easily felt 

 in passing the finger from the occiput outwards. By making 

 an incision between this process and the occipital spine, the 

 nerve can be very easily found. The other nerve (n. auricu- 

 laris magnus, see fig. 226) springs from the anterior branches 

 of the second and third cervical nerves ; it becomes superficial 

 at the posterior edge of the sterno-mastoid, and then runs up- 

 wards, covered only by integument, towards the thin edge of 

 the external ear, where it soon divides into two branches. It 

 is most easily found at the root of the ear, just before it di- 

 vides. 



The animal having been curarized, the apparatus for artificial 

 respiration is connected with the trachea, and the manometer 

 of the kymograph with the carotid artery. The great auricu- 

 lar nerve is then carefully exposed, separated from the sur- 

 rounding parts with the aid of two pairs of blunt forceps, and 

 divided. The next step is to arrange the lobe of the ear in 

 such a way that the central artery can be well seen. With 

 this view, if sunlight is not at command, a paraffin lamp 

 should be so placed that its light may be thrown on the ear 

 from behind by a condensing lens, while the lobe itself is sup- 

 ported vertically by a suitable holder. Before beginning the 

 experiment, the central arteiy should be carefully observed, 

 attention being particularly directed to the rhythmical changes 

 of diameter which it undergoes. Its condition having been 

 carefully noted, and a preliminary kymographic tracing having 

 been taken, for the purpose of preserving a record of the pre- 

 vious arterial pressure, the central end of the nerve is laid 

 upon the points of the excitor, and the key opened for a couple 



