CHAPTER XXXVI. 



CEREBRAL LOCALIZATION, DECEREBRATE RIGIDITY, 



RECIPROCAL INNERVATION, FUNCTIONS OF 



SPINAL ROOTS IN THE MAMMAL (DOG.) 



Demonstration 15. 



A tracheal cannula is inserted in an etherized dog, and ligatures placed loosely 

 around the carotid arteries on both sides. With the animal in the prone position 

 the head is raised by placing a pad under it, being careful to see that there is no 

 kinking of the tube leading from the tracheal cannula to the ether bottle. To 

 serve as a landmark for the crucial sulcus of the cerebrum (which corresponds to 

 the Rolandic fissure on the human brain) two threads are stretched across the 

 head, one of them joining the outer canthi of the eyes and the other, the condyles 

 of the lower jaw. The crucial sulcus lies a little behind the mid-point between 

 the two threads. An incision is made along the mid-line of the scalp and by blunt 

 dissection the temporal muscle is separated from the bone far enough to make 

 room for two trephine holes one in front of the other and with their inner margins 

 at least 3 mm. from the mid line so as to avoid wounding the superior longitudinal 

 sinus. To manipulate the trephine, the steel point is first of all adjusted so that 

 it projects beyond the sawing edge, and this point is bored into the skull in order 

 to afford good fixation. When the sawing edge reaches the bone, care is taken it 

 cuts uniformly, and when a good start has been made the central point is pulled 

 up so that this may not puncture the brain The trephining is continued until 

 the inner table of the skull is cut through around most of the circle, the trephine 

 is then removed, and the disc of bone pried up by means of a pereosteal elevator 

 or a stout pair of forceps. There is apt to be considerable haemorrhage at this 

 stage, but it can usually be controlled by applying for a few minutes a pad of 

 gauze thoroughly wrung out with hot isotonic saline. When the two trephine 

 holes have been made they are connected together by bone forceps, taking care 

 not to wound the brain and controlling bleeding with hot gauze. A curved sur- 

 gical needle is passed through the dura and by means of it the latter is raised 

 sufficiently so as to be able to cut it with a sharp pointed scissors. The exposed 

 brain should be covered with gauze soaked in isotonic saline. 



In order to stimulate the cortex a large plate (indifferent) 

 electrode is placed on the moistened skin of the lower dorsal region 

 and connected with one terminal of the secondary coil of an in- 

 ductorium with the other terminal of which a blunt-pointed 

 (stigmatic or diagnostic) electrode is connected. 



Having made a rough sketch indicating the position of sulci and 



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