THE INSULA OF THE PIG. 

 By T. E. Clark. 



With Plate I. 



The insula (island of Reil) of the pig (S?ts scrofd) is located 

 between the frontal, parietal and temporal lobes and the olfac- 

 tory tract. ^ A small portion of this area is included in the Syl- 

 vian fissure, but by far the greater part, as in the sheep, lies in 

 what some authors call the vallicula or Sylvian fossa (rhinal fis- 

 sure. Turner), cephalad of the temporal lobe and dorsad of the 

 enormously developed olfactory tract. The operculums are not 

 well developed and if present at all are very rudimentary. Lus- 

 sana and Limoigin say they are wanting in the pig. ^ In at least 

 three-fourths of the 20 brains examined, a fissure was found at 

 P. (see Figs. 2 and 4,) and I have assumed it to be constant in- 

 asmuch as the brains in which it was wanting were those of pigs 

 under one year old. This fissure, although rudimentary, is well 

 defined and may be the rudiment of the presylvian. 



The insula is entirely overlapped dorsally and, when con- 

 cealed, is also covered laterally by the area in figs. 2 and 4. 

 Its cephalic portion is somewhat concealed by the area N (fig. 

 2). Accordingly I have concluded that the operculum (m) and 

 the prae-or sub-operculum (n) are sometimes present though 

 rudimentary. 



Professor Sir Wm. Turner^ names the fissure dorsad of the 

 olfactory crus (ex, fig. i) the rhinal fissure (r). This fissure 

 may be no other than the rhinal fissure if the frontal and par- 

 ietal lobes are so developed as to completely overlap the insula 

 laterally, as the Sylvan fossa will then be closed up and the 

 rhinal fissure would extend to the surface as in fief. i. How- 



I. Fisiologia der Centri Nervosi Encefalici, Vol. I, p. 150. 

 3. The Convolutions of the Brain, p. 35, Fig. 29. 



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