x PRACTICAL DIRECTIONS 473 



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 vertebne), 

 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 turpentine 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. 



\Yith 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 and in longitudinal sec- 

 tion, 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 fine nails 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 vagus nerve on its walls ; 

 the wide intestine, narrowing into a short rectum posteriorly ; 

 PRACT. ZOOL. G G 



