INSPECTION OF TSE AMPHIBIAN BRAIN. 419 



A, PI. II ; Wyman, 34, PI. I ; Duges, 4, PI. 10 ; Bourgery and Jacob, A, VIII, PI. 22, 

 Fig. 7 ; Owen (Linnean Transactions, XVIII, PI. 27). 



§ 1094. Instruments and Materials. — Tripod magnifier; fine 

 forceps ; beaded bristles ; small disli of 62-67 per cent, alcohol or 15 

 per cent, glycerin in which, the brain may be dipped, or a vial of the 

 same with a quill duster for applying the liquid. 



Keep the brain wet with the alcohol or glycerin. 



Kemove the white masses of calcareous crystals at the side of 

 the caudal region. 



Cpmpare the several regions with Fig. 110, or with figures in 

 other works {§ 1093). 



§ 1095. Note the lateral expansion of the myelon to form the 

 metencephalon (medulla), abrupt in the frog, very gradual in Men- 

 obranchus. 



Note the pigmented metatela which forms the dorsal surface of 

 the metencephalon. 



If the metatela is in place, its cephalic border more or less com- 

 pletely covers the cerebellum. Grrasp its sinistro-cephalic angle 

 with the forceps and invert it gently until it lies dextrad of the 

 metencephalon. Note its thickness as compared with the myelonal 

 pia, and the symmetrical corrugation of the ental surface. The 

 cavity thus exposed is the metacoelia (ventriculus quartus). 



In Menobranctus the metacoelia is much elongated, and the caudal part of the meta- 

 tela is very thin. 



Cautiously remove the arachnoid from the dorsal aspect of the 

 entire brain, excepting just between the divergent caudal ends of 

 the hemispheres ; it is little if at all pigmented, and bridges the 

 interhemispheral fissure as shown in Fig. 112, H. 



The widest region is the mesencephalon {optici), the pia of 

 which is thickly pigmented. Note the marked mesal furrow be- 

 tween the two lateral convexities, and that the longer axes of the 

 latter diverge cephalad. 



In Menobranchus the mesencephalon is but little wider than the adjoining segments, 

 the mesal furrow is very shallow, and the lateral masses hardly merit the name of lobes. 



Between the optici and the metacoelia is a narrow transverse 

 band, unpigmented and with its caudal margin dorsiverted, and 

 separated from the optici by a somewhat deep furrow. This is the 

 cerebellum, the dorsal part of the epencephalon. 



