150 . APPENDIX 



stroke of the mallet will of course follow the direction thus set. The direction is nearly 

 vertical. Three smart mallet-strokes on the knife-handle suffice for the severance of the 

 head. Under the deep anaesthesia the severance causes no spasm or convulsion. If 

 the knife-blade is suitably sharp the respiratory movements are usually not interrupted, but 

 if the knife is not sharp there is more concussion and respiration may stop. The respiration 

 is more likely to be interrupted m old animals than in young. 



ix. The head having been thus separated, the preparation is lifted from the decerebrator. 

 It is best lifted by holding the neck between thumb and finger close behind the wings of 

 the atlas, thus compressing the vertebral arteries (see text-fig. 47). The preparation is placed 

 on the experiment table. The occipital stump is supported above the rest of the carcase 

 by a string loop passed through the skin of the stump and slung on the cross-piece 

 of a standard. A pledget of dry cotton wool is laid against the base of the posterior 

 colliculus where that has been cut through, to allay haemorrhage. The preparation can be 

 lowered to horizontal on the table without haemorrhage in about 5' and is then ready for 

 use. If one of the carotids has been merely looped, not ligated, it can be gently released, 

 attention being paid to whether there is recurrence of haemorrhage or no. Haemorrhage 

 from the base of the cut neuraxis can always be controlled by temporary compression of the 

 vertebrals behind the lateral wings of the atlas (see above, p. 138). 



The severance effected by the decerebrator takes the line v-v in text-fig. 47. It removes 

 the head along a coronal plane sloping from near the inion past the mandibular joint and 

 emerging into the mouth through the coronoid processes of the lower jaw. The rest of the 

 mandible, and the tongue protected by the tongue-guard of the decerebrator, remain intact. 

 The plane passes between cerebrum and cerebellum, shaving off usually from the former the 

 extreme posterior tip of the occipital lobes, which lie loose in the remnant of skull, and 

 taking usually from the latter the frontmost piece of its median lobe along with a median 

 slip of the bony tentorium. The hemispheres and basal ganglia of the cerebrum and both 

 the colliculi are removed with the head. 



Employment of the decerebrator presents several advantages. It is speedy ; after the 

 animal has been anaesthetized the procedure occupies about four minutes. There is greater 

 regularity of the level of severance than is easily attainable by the ordinary operative 

 procedure. The total removal of the head except for a remnant of the occiput and of the 

 lower jaw leaves no room for doubt that the whole cerebrum and brain back to the pons 

 have actually been ablated, and that the preparation is merely a temporarily surviving 

 carcase. Under conditions where the teacher may find himself obliged without skilled 

 assistance to make ready the preparations for his class he can, using the decerebrator, do so 

 single-handed without risk of failure, and speedily, although not so speedily as if a skilled 

 assistant co-operated. If an assistant is available he can usefully compress the vertebrals 

 (text-fig. 47) between finger and thumb behind the atlas wings as the preparation lies in the 

 decerebrator at the moment of actual severance of the head (§ viii). The decerebrator has been 

 employed for provision of the class preparations now for upwards of five years, and has 

 worked satisfactorily in the hands of all who have employed it. 



Obs. 54-7. In providing the decerebrate preparation for this exercise the tracheal 

 cannula should be introduced well posterior to the cricoid and its projecting limbs be short ; 

 more room is thus given for the student's dissection. The carotid of the side on which the 

 gland is to be used should not be ligated but merely looped, so as to be controlled at the 



