962 THE CENTRAL NERVOUS SYSTEM 



head, an incision made in the middle line through the skin, and the flaps 

 reflected so as to expose the 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 Djambi, which should be removed in a few 

 minutes, the wound cleansed with iodoform gauze wrung out of physio- 

 logical salt solution at 50* C., and sewed up. Study the phenomena 

 described on p. 915. 



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

 brain of a dog, noting especially the crucial sulcus (Fig. 367, p. 917), 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 these 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 wounding the longitudinal 

 sinus. Carefully work the trephine through the skull, taking care not 

 to press heavily on it at the 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. 918) may also be employed. Contraction of 

 the corresponding groups of muscles will 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 opportunity 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 a.nimal can be used for stimulation of the 

 spinal nerve-roots, as described in Experiment I (p. 957). 



* It is not necessary to remove the dura mater. 



