FEATURES OF THE MAMMALIAN BBAIiV. 439 



THE ENCEPHALIC SEGMENTS IN THE CAT. 



§ 1130. The recognition of the several segments is less easy than 

 with the frog in some respects on account of certain features of the 

 mammalian encephalon. 



§ 1131. Differences between the Bredns of the Cat and the 

 Trog. — In a general way these have been indicated alread/(§§ 1055, 

 1056) ; they may be more deiinitely stated as follows : — 



(1) In the cat the coelise are irregular in form and relatively 

 reduced in extent (Pig. 113 ; PL II, Fig. 4). 



(2) The parietes are relatively thicker, and moi:e diflferentiated 

 as to both contour and structure (Fig. 113 ; PL II, Fig. 4 ; PL III, 

 Fig. 13). 



(3) With several segments the dorsal portion (roof) is much 

 more extensive than the ventral (floor), (Fig. 117 ; PL II, Fig. 4). 



(4) The longitudinal axis of the entire brain presents a decided 

 flexure, the convexity of which is dorsal and coincides in position 

 nearly with the mesencephalon (Fig. 88). 



(5) The dorsal portions of two segments (epencephalon and pros- 

 encephalon) are so greatly enlarged as to cover all the others except- 

 ing parts of the metencephalon and rhinencephalon, the extremes 

 of the series (Fig. 88, 104, 117 ; PL I, Fig. 1, 2). 



(6) In addition to the Amphibian commissures (cMasma, postcommissura, prmeommis- 

 sura), there are in the oat's brain more or less distinct fibrous fasciculi constituting other 

 commissures — longitudinal (Crura cerebri, PI. II, Pig. 3, PI. Ill, Fig. 11 ; Crura olfactoria, 

 PI. II, Fig. 3, 4 ; postpedunculi, praepedunculi) ; transverse (pons, Fig. 117 ; PI. II, Pig. 3, 

 pn. ; decussatio pyramidum, medipedunculi, Commissura fornicis, PI. IV, Pig. 14, cs.f) ; 

 and oblique (fornix, PI. IV, Fig. 14,/.). 



(7) Between the apposed surfaces of the thalami is established a connection, the medi- 

 commissura (Fig. 133; PI. II. Fig. 4, mcs.), which occupies a large portion of the diacoelia. 



(8) The apposed surfaces of the hemispheres are connected along a slightly curved line 

 by a thick band of fibers, the callosum (Pig. 104, 115 ; PI. Ill, Pig. 13, PI. IV, Fig. 15, d.), 

 the largest and presumably the most important of the commissures. 



(9) The dorsal aspect of the mesencephalon presents a transverse furrow, distinguish- 

 ing a cephalic pair of lobes, the optici proper, from a caudal pair, the postoptici (Fig. 

 114; PI. Ill, Pig. 7); hence the bigeminum of the frog becomes the quadrigeminum of 

 the cat. 



(10) The lateral aspect of the diencephalon presents at least two elevations, postgenic- 

 ulatum and praegeniculatum (PI. Ill, Fig. 7, 9, pgn., prgn.). 



(11) Of the diaccelian roof, the membranous part {diatela, PI. Til, Pig. 10) is relatively 

 more extensive, while the nervous part (postcommissura, PI. II, Pig. 4, pea.) is corre- 

 spondingly diminished ; concomitantly the conarium is attached near the caudal end of 

 the diencephalon and is retroverted so as to rest upon the mesencephalon. 



