414 ON SOME FUNCTIONS OF THE ENCEPHALON. 



striata, with the small optic thalami Th. between them and 

 the optic lobes. 



The position of the optic lobes pretty well corresponds to 

 the hind part of the fronto-parietal bones, which are distinctly 

 seen when the skin over the skull is removed. A transverse 

 incision made through the skull with a narrow strong blade, 

 in a line which runs as a tangent to the anterior borders of 

 the incmbraniB tympani, will separate the cerebral from the 

 optic lobes. This may be done without removing even the 

 skin. In most cases, however, it is better to remove the roof 

 of the skull and to see the parts of the brain which are being 

 operated on. 



The frog being placed under chloroform, make a longitudi- 

 nal incision over the mid-line of the skull from behind the 

 nose backwards, and convert it into a T incision by a trans- 

 verse cut immediately behind the raembranse tympani (fig. 2C.O, 

 e.fab.). Hook back the flaps. With a pair of fine bone 

 forceps or strong scissors cut right across the fronto-parietal 

 bones where the}' overlap the ethmoid. Each bone may then 

 be easily seized by its front end and torn away without any 

 injury to the cerebrum below. That being done, the blade of 

 a pair of scissors may be carefully slipped under each parietal 

 bone close to its external border and the bone cut through. 

 The bones may then be carefully seized at their front border 

 with a pair of forceps, lifted up and torn away. If the blood- 

 vessels at the side have been avoided, there will be but little 

 bleeding, and what does occur will soon cease. The cerebrum 

 may now be simply divided from the optic lobes by a trans- 

 verse incision and removed. A better method, in order to 

 prevent any injury to the optic nerves and optic thalami, is to 

 cut across the cerebral lobes at their junction with the olfac- 

 tory lobes, fig. 296 L. ol., to lift up their cut ends and so to 

 remove them carefully, working gradually backwards. To 

 separate the optic lobes from the medulla, nothing more than 

 a simple transverse incision is necessary, taking care not to 

 injure the cerebellum ; but it is as well to remove all the parts 

 in front of the incision. The flaps of skin may then be 

 brought together and united by a couple of sutures, and the 

 animal left to recover from the operation. All plugging, etc., 

 should be avoided. 



oh*. I. The phenomena of a frog when the animal possesses 

 /fa' medulla oblongata and cerebellum as well as the spinal 

 cord, but all the rest of brain has been removed. The follow- 

 ing facts may be observed after the animal has completely 

 recoversd from the operation, and should be compared with 

 the phenomena of a frog possessing a spinal cord only. 



The attitude is completely normal, quite different from that 



