1879.] NATURAL SCIENCES OF PHILADELPHIA. 429 



complicated arches." The primary fissures, according to him, are 

 the anterior and posterior branches of the fossa Sylvii ; the fissura 

 centralis or fissure of Rolando, fissura perpendicularis interna or 

 parietooccipital fissure, fissura parallela or superior temporal 

 fissure, and the fissura hippocampi. This latter fissure of Bischoff 

 corresponds to Gratiolet's fissure des hippocampes. and includes 

 both the fissura hippocampi and the fissura calcarina of other 

 writers. The type is expressed, according to Bischoff, by these 

 fissures, and the development of the convolutions consists merely 

 of arched windings surrounding the ends of these primary fur- 

 rows, and the further development of the convolutions arises in 

 fact through the stronger development, bending backwards and 

 forwards, rising and sinking of the lobules around the above-named 

 furrows. Through this process there arise secondary folds and 

 fissures, side convolutions and connections and separations of in- 

 dividual convolutions. The same, says Bischoff, may be different 

 on the two sides of the same brain and in different individuals, 

 the ground forms being, therefore, more or less hidden, but we 

 can recognize them easily in all brains. He hopes, however, that 

 it will soon be possible to explain and make intelligible these in- 

 dividual modifications. There are, however, convolutions which, 

 as Bischoff remarks, do not appear to be in unison with this type, 

 such as the first and second frontal and the convolutions of the 

 occipital and temporal lobes. For these Bischoff says that he can 

 find no particular plan on which they may be based. They arise 

 one after the other, and become more and more complex, as it 

 appears, from purely mechanical necessities of the surface increas- 

 ing in a definite space. In tnis manner arise the first and second 

 frontal fissures, the second temporal, fissura collateralis, etc., and 

 their bordering convolutions. Thus, in the frontal lobe, Bischoff 

 points out two upper frontal convolutions, and a third or inferior 

 arching around the ascending branch of the fossa Sylvii. In the 

 frontal lobe an anterior and a posterior central winding arching 

 around the upper and lower extremities of the fissura centralis. 

 Posterior to these, at the upper border of the hemisphere and ex- 

 tending; over on to the mesial surface, a superior internal parietal 

 group of convolutions (obere innere Scheitelgruppe) correspond- 

 ing to the lobulus parietalis superior and precuneus. Besides 

 these, Bischoff points out five so-called arched parietal convolu- 

 tions. A first or anterior parietal arched convolution (erste oder 

 vordere Scheitelbogenwindung) surrounding the upper extremity 

 of the horizontal branch of the fossa Sylvii. A second or middle 

 (zweite oder mittlere Scheitelbogenwindung) surrounding the up- 

 per extremity of the superior temporal fissure. Posterior to these 

 a third smaller arched convolution which curves around the upper 

 end of the fissura temporalis media, the dritte Scheitelbogenwin- 

 dung. He admits, indeed, that the arrangement of these arched 

 convolutions is very variable and manifold, and therefore the 



