498 ANATOMICAL TMCSNOLOGT. 



splenium, however, it presents a short and quite sharp cephalic convexity. The cinerea 

 cephalad of the F. hypocampm constitutes the fasciola. 



§ 1351. F. Sylviana, F. 8., the Sylvian fissure.— Fig. 124; PL I, Fig. 2; PI. II, 

 Fig. 3 ; PI. Ill, Fig. 5 ; § 1163. 



Syn. — Fissura Sylvii ; the " posterior " or longer branch of the human F. Sylvii. 



By common consent, this short and distinct, fissure of the cat and dog is called by the 

 name originally applied to the much more extensive and complex human fissure. To dis- 

 cuss the homology would occupy undue space. The chief questions are (1) as to the rep- 

 resentation of the insula (§ 1247), which in man is concealed between the dorso-cephalic 

 and the ventro-caudal lips of the fissure ; and (2) as to the correspondence of the relatively 

 extensive region between the F. Sylviana and the F. superorbitaZis with the human oper- 

 culum ; Meynert, 1, Fig. 16; Wilder, 11, 225, and 14, 551. 



§ 1352. The statement (11, 223) of the senior author as to the presence of the Sylvian 

 fissure in all brains which are fissured at all (quoted in the last two editions of Dalton's 

 Physiology, A, 413) referred originally only to the lateral fissures, and may not be correct 

 with even that qualification, for the rhinalis and posMiinalis seem to occur in some mam- 

 mals when the Sylvian is either absent or very indistinct. 



§ 1353. Fissura ansata, F. «?i.— Fig. 24 : PI. I, Mg. 1, 2. 



This fissure is peculiar and presents some difllculties. Most commonly it seems to 

 form simply a conjunction between the lateralis and the coronalis, with a branch pointing 

 meso-cephalad. Less frequently is it independent of the coronal, as in PI. I, Fig. 2, and 

 the left side of Fig. 1 ; most rarely is it wholly isolated as a simple diagonal fissure, as in 

 Fig. 21 and the right of PI. I, Fig. 1. Nevertheless, Krueg and the senior author came 

 independently to the conclusion that this is the primitive condition of the fissure and the 

 one to be represented upon a diagram. 



§ 1354. Fissura anterior, F. a.— Fig. 24 ; PI. I, Fig. 1, 2; PI. Ill, Fig. 5. 



The disconnection of the dorsal end of this fissure from that of the postiea, so that the 

 keystone of the first arch is absent, constitutes a constant distinction between all the 

 Felidae and the feral Canidse and most domestic dogs. The two fissures sometimes 

 approach quite closely and even overlap, but we have never observed a junction. On the 

 other hand, while the two form a continuous fissure in all feral Canidse and most domesti- 

 cated dogs, in the latter the arch is sometimes broken, giving this region of the brain a 

 feline aspect (Wilder, 11, 229, and Fig. 13, 16). In this as in other respects, the dog dis- 

 plays more variability than the cat. 



§ 1355. Fissura cruciata, F. cr.— Fig. 117, 124, 125 ; PI. I, Fig. 1, 2 ; PI. II, Fig. 4; 

 PI. Ill, Fig. 5 ; PI. IV, Fig. 16-19. 



§ 1356. Constant and Peculiar Characters. — Indents the dorso-mesal margin of the 

 hemisphere near its cephalic end, so as to appear upon both the dorsal and mesal aspects. 

 Length of the dorsal and mesal portions approximately equal. Dorsal portion at a right 

 angle with the meson. Line formed by the dorsal portions of the two fissures about one 

 half the length of the line representing the F. interhemispheralis, with which it forms a 

 Roman cross. Lateral end simple and independent. 



§ 1357. Variable Characters. — Caudal end of mesal part of fissure usually dorsad of 

 the junction of the cephalic and middle thirds of the callosum, and about two fifths of the 

 distance from the callosum to the dorsal margin of the hemisphere, thus about midway 

 between the callosum and the cephalic end of the F. splenialis. Rarely are these two 

 fissures continuous. 



§ 1358. The dorsal part of this fissure is a marked feature of the dorsal and cephalic 

 aspects of the hemisphere, on account of its straightness, simplicity and independence, and 



