46 DON TUCKER 



TORTOISE 



The head of a tortoise preparation is shown in Fig. 1, which is to orient 

 the openings shown in greater detail in Fig. 2. In the trephined opening the 

 main and accessory olfactory bulbs and the intracranial portions of the 



Fig. 1. Experimental arrangement for neural recording. The view of the tor- 

 toise's head is from above and in front. 



olfactory and vomeronasal nerves are visible. The cut edges of the dural 

 and pial membranes may be seen also. In the nasal exposure strands of 

 olfactory nerve are prominently visible through the intact cartilage of the 

 nasal capsule. Olfactory and vomeronasal twigs may be picked up intra- 

 cranially, but trigeminal twigs must be got from within the capsule. For 

 this purpose the trephine opening is advanced to overlap the rear of the 

 nasal cavities. A prominent branch of the trigeminal nerve enters the 

 nasal capsule ventrolaterally to the olfactory nerve and then curls up 

 around it, splaying out in numerous branches distributed to the dorsal and 

 medial nasal mucosa and to tissues external and anterior to the capsule. 



Basic Techniques 



Twigs from the medial part of the olfactory nerve project to the septal 

 mucosa. With a window to the olfactory cavity as in Fig. 1, a stimulating 

 electrode may be introduced and the mucosa explored for responses in a 

 twig on the recording electrodes (Fig. 3). Alternatively, the intracranially 

 situated twig may be stimulated electrically and the distribution of the 

 antidromic compound action potential mapped on the mucosa. The 

 olfactory receptors associated with a small twig of the nerve often fall in a 

 slightly elongated area of less than one square millimeter. 



