* APPEXDIX. 537 



cloth. When first seized, the caudal end of the frog should be held downward or away 

 from the operator, so that the urine may not be discharged upon the clothes. 



To pith, ventriduct the head with the index, and pass the tip of the right index from 

 between the eyes caudad until a distinct depression is felt at the meson, upon a line corre- 

 sponding nearly with the caudal margins of the membranie tympanorum. With a 

 sharp-pointed Charriere scalpel, divide the skin transversely for about 3 mm., and then 

 plunge the scalpel deeper so as to divide the " medulla." Respiratory movements cease, 

 and the frog is supposed to be dead and incapable of feeling. 



If the cephalic portions of the brain are wanted, the head should be cut off and the 

 brain exposed without delay (§ 1087) ; or reflex movements of the limbs should be pre- 

 vented by breaking up the myelon with the piobe or a piece of wire introduced from the 

 incision into the neural canal. 



§ 1454 (§ 1115). Macrotome. — This name is applied to a simple apparatus upon which 

 sections of the head or other parts may be made with a saw. It is, in effect, a kind of 

 " miter-box," and is made as follows : — 



A block of hard wood (ash, oak, etc.), 6 cm. thick and about 18 cm. long, has a rebate 

 (" rabbet ") cut out along one of its long corners to a depth of 12 mm., and is then accu- 

 rately divided at about the middle of its length. 



The pieces are then to be screwed securely across a perfectly level board, about 36 x 18 

 cm., at about 10 cm. from one end. The pieces are to be separated by only the thickness 

 of the blade of the small back saw (§ 152) used in making the sections, and the rebate is 

 to be above, toward the shorter portion of the board. 



At the right of the division between the blocks (or at the left if the operator is left- 

 handed) is to be placed a block about 4 cm. thick ; it is to be adjustable by means of a 

 thumb-screw passing through a slot. In § 1117, this block is called the slide ; in some 

 cases it may be dispensed with. 



The macrotome may be used not only for hemisection of the head, but also for making 

 frozen sections of limbs and other parts. The saw should be kept sharp, and clean but 

 not oily. 



§ 1455 (g 1371). The Brains of the Lower Vertebrates. — The brains of Amphibia 

 and of the air-breathing Vertebrates (Reptiles, Birds and Mammals) are readily compara- ' 

 ble with that of the frog or Menobranchus. But those of the " fishes " (sharks, skates, 

 lamprey-eels, Ceratodus, gar-pikes and Teleosts) have not yet been homologized satis- 

 factorily, and the beginner is not advised to undertake their examination ; some idea 

 of the difficulties may be gained from the special papers by various writers upon the brains 

 of the several groups and from a brief summary by the senior author {2(i). 



§ 1456 (§ 318). The Use of Mica for Mounting Alcoholic Specimens. — Prof. Leslie 

 A. Lee has kindly called our attention to the use of slips of mica for the mounting in alco- 

 hol of preparations which require some support. It can readily be cut into the desired 

 shape, and holes can be drilled through which may be passed the threads for supporting 

 the specimen. 



§ 1457 (§§ 1128, 1138, 1238). The Fornix.— According to an editorial in the Am. Jour, 

 of Neurology and Psychiatry (I, 402), there are two fornices, right and left, one for each 

 hemisphere, as there are two fimhrice, etc. This commends itself to us upon some grounds, 

 but the commonly accepted view should not be hastily abandoned. 



