IX PRACTICAL DIRECTIONS 457 



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

 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. 419 — 427, 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. 445 — 447). 



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

 the cranium in longitudinal section ; {6) trunk- and caudal vertebrre 

 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 (see 

 p. 456) 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. 397). 

 Make out : — 



1. The liver, with ^e gall-bladder-'paxily embedded in it close to the 

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

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

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

 and rectal gland ; and the incomplete mesentery. Pass a seeker back- 

 wards, on one side of the cloaca, through an abdominal pore. 



2. In the male, the spermaries, fused together posteriorly ; and in the 

 female, the single ovary and the oviducts and shell-glands. The peri- 

 toneum covering the kidneys is so thick that at present they can only be 

 recognised as slightly convex ridges. 



II. — Remove the skin from the dorsal surface of the head between and 

 slightly in front of and behind the eyes, and then slice away part of the 



