PRACTICAL EXERCISES 889 



skull. Cut through the bones with scissors, and make a sufficiently 

 large opening to bring the cerebral hemispheres into view. They are 

 now rapidly divided from the corpora bigemina and lifted out with 

 the handle of a scalpel. The bleeding^is very free, but may be 

 partially controlled by stuffing the cavity with the vegetable fibre 

 known as Pengavar D iambi, which should be removed in a few 

 minutes, the wound cleansed with iodoform gauze wrung out of 

 physiological salt solution at 50 C., and sewed up. Study the 

 phenomena described on p. 841. 



i2. Stimulation of the Motor Areas in the Dog. (a) Study a 

 hardened brain of a dog, noting especially the crucial sulcus (Fig. 349, 

 p. 843), the convolutions in relation to it, and the areas mapped out 

 around it by Hitzig and Fritsch and others, (b] Inject morphine under 

 the skin of a dog. Set up an induction-coil arranged for tetanus, 

 with a single Daniell in the primary circuit. Connect a pair of 

 fine but not sharp-pointed electrodes through a short-circuiting key 

 with the secondary. Fasten the dog on the holder, belly down, 

 and put a large pad under the neck to support the head. Clip the 

 hair over the scalp. Feel for the condyles of the lower jaw, and 

 join them by a string across the top of the head. Connect the 

 outer canthi of the eyes by another thread. The crucial sulcus 

 lies a little behind the mid-point between thess two lines. Now 

 give the dog ether, make a mesial incision through the skin down 

 to the bone, and reflect the flaps on either side. Detach as much 

 of the temporal muscle from the bone as is necessary to get room for 

 two trephine holes, the internal borders of which must be not less 

 than inch from the middle line, so as to avoid wounaing the longi- 

 tudinal sinus. Carefully work the trephine through the skull, taking 

 care not to press heavily on it at ths last. Raise up the two pieces 

 of bone with forceps, connect the holes with bone forceps, and 

 enlarge the opening as much as may be necessary to reach all the 

 ' motor ' areas. At this stage only enough ether should be given to 

 prevent suffering. Now unbind the hind and fore limbs on the side 

 opposite to that on which the brain has been exposed, apply blunt 

 electrodes successively to the areas for the fore and hind limbs, 

 and stimulate.* The ' unipolar ' method of stimulation (p. 843) 

 may also be employed. Contraction of the corresponding groups 

 of muscles wilf be seen if the narcosis is not too deep. Movements 

 of the head, neck, and eyelids may also be called forth by stimulating 

 the 'motor' areas for these regions. Stimulation in front of the 

 crucial sulcus may also cause great dilatation of the pupil, the iris 

 almost disappearing. The dilatation takes place most promptly, 

 and is greatest on the opposite side, but the pupil on the same side 

 is also widened. Even after section of both vago-sympathetic 

 nerves in the neck, a slow and slight dilatation, greatest perhaps 

 on the same side, may be caused by cortical stimulation. Repeat 

 the whole experiment on the opposite side of the brain. In the 

 course of his observations the student will perhaps have the oppor- 

 tunity of seeing general epileptiform convulsions set up by a localized 

 excitation. They begin in the group of muscles represented in the 

 portion of the cortex directly stimulated. After the convulsions 

 have been sufficiently studied, they should be again induced, and 

 the stimulated ' motor ' area rapidly excised during their course. In 

 some cases this will be followed by immediate cessation of the 

 spasms, (c) The same animal can be used for stimulation of the 

 spinal nerve-roots, as described in Experiment i (p. 885). 

 * It is not necessary to remove the dura mater. 



