EXPOSURE OF THE BRAIN. 427 



tween the nippers. It may be removed in small pieces, so as to 

 save the NN. facialis and auditorius which enter the Meatus 

 auditorius internus, and the little Lobulus appendicularis of the 

 cerebellum which is lodged in a slight fossa (Fs. ap.) just dorsad 

 of the meatus (Fig. 59, M. a. ?'.). 



Since no nerves are transmitted by the mesal region of the basis 

 cranii, it may be removed with comparative freedom as far cephalad 

 as the sella (Fig. 59), where some care is needed to avoid injuring 

 the hypophysis (Fig. 88, Hy.}. 



The skull may now be held more securely by the facial region, 

 especially if a towel is employed. In removing the bone at each 

 side of the meson, and just cephalad of the bullse, great care is 

 required to disengage the nerves which emerge by the Fm.Fm. ovale, 

 Totundum and lacerum anterius. These nerves, the NN. oculomo- 

 torius, trocJilearis and abducens, with the ophthalmic, superior 

 maxillary and inferior maxillary divisions of the N. trigeminus, 

 penetrate the bone more or less obliquely, and are closely sur- 

 rounded by dense connective tissue. 



The entire maxilla is now to be removed by first nipping the 

 interorbital region just cephalad of the fronto-maxillary suture, and 

 then, with the bone scissors, cutting toward this point from just 

 caudad of the cephalic root of the zygoma. The scissors should be 

 kept as far cephalad as possible, so that the Lobi olf actor ii may 

 not be injured. This plan serves equally well for some dogs, but 

 with the larger breeds, which have prominent olfactory lobes, the 

 interorbital region should be nipped at about the middle of the 

 length of the nasal bones. 



1103. Remove the mesal wall of the orbit and the turbinated 

 bones, using care not to crush the very soft Lobi olf actor ii. The 

 olfactory nerves should be divided, a few at a time, with the scissors 

 or the tip of the scalpel, and all pulling and twisting of the parts 

 must be avoided. , 



The large and white Nerm optici will have been seen in the 

 orbit, and should be divided near the bone. In removing the plate 

 (Fig. 60) upon which the chiasma rests, use care not to pull upon 

 it, lest the terma or other delicate parts should be torn. 



During the remaining steps of the operation, the head must be 

 held by the parietal regions, and with great care, so as to avoid 

 pressure of the tips of the fingers upon the brain. The bone also 

 must now be cut by the nippers rather than twisted or broken. 



