x PRACTICAL DIRECTIONS 473 



weak spirit or formaline, and not allowed to dry, or the cartilages will 

 of course shrink, unless the following method is resorted to : 



Thoroughly clean a skeleton, or typical parts of it (e.g. skull, limb- 

 skeleton, and a few trunk- and caudal vertebrae), and then transfer from 

 ^ weak into strong methylated spirit for a day or so, and afterwards into 

 absolute alcohol for a few hours. Place in a vessel filled with turpen- 

 tine for another day, and then transfer into melted paraffin in the water- 

 bath until the parts are thoroughly permeated, after which they should 

 be suspended in the water-bath in order to drain off the superfluous 

 paraffin, and then allowed to cool. Any superfluous paraffin still 

 remaining may then be removed with a hot wire. 



With the specimens before you, work through pp. 435-443, noting 

 first of all the relations of the parts in the entire skeleton (viz., cranial 

 and visceral portions of the skull, trunk- and caudal vertebrae, and the 

 skeleton of the median and paired fins). When examining the skull, 

 note the nerve foramina (pp. 461 and 463). 



Sketch (a) the skull (including visceral arches) from the side, and 

 the cranium in longitudinal section ; (b] trunk- and caudal vertebrae 

 from the side or in longitudinal section and from the anterior or 

 posterior face ; (c] the pectoral arch, from the side, with the pectoral 

 fin attached ; and (d] the pelvic arch and fin. 



C. General dissection: Enteric Canal, &c. 



I. Fix the animal down on the dissecting board with the ventral 

 surface uppermost, by means of strong pins inserted through the 

 paired fins, and make a median longitudinal cut with a common knife 

 through the skin and underlying muscular layer which is closely 

 connected with the skin, from the pectoral to the pelvic arch. At 

 each end of this incision cut through the body-walls transversely, and 

 reflect and pin down the two flaps. Cut through the pelvic arch 

 slightly to one side of the median line, so as not to injure the cloaca. 

 The abdominal cavity, lined by the peritoneum, will then be exposed. 

 (In the course of your dissection you will probably find many parasitic 

 thread-worms belonging to the phylum Nemathelminthes (see p. 412). 

 Make out (compare Fig. 117) : 



I. The liver, with the gall-bladder partly embedded in it close to the 

 junction of its two lobes ; the gullet, U-shaped stomach, and the 

 branches of the vagtis nerve on its walls ; the wide intestine, narrow- 

 ing into a short rectum posteriorly ; the cloaca ; the pancreas, spleen, 



