294 PRACTICAL LESSONS IN SCIENCE. 



into the stomach; trace the intestine from the stomach to the 

 anus, and notice the delicate membrane called the mesentery. 

 Near the intestine find a reddish body, the spleen. Find the air 

 bladder', it sometimes communicates with the alimentary canal. 

 Does it in this case? Above the air bladder find two slender, dark 

 red bodies, the kidneys, and in the posterior part of the body 

 cavity find the urinary bladder and the reproductive organs; 

 the yellow single or double ovary with the oviduct in the female, 

 and the two white testes in the male. 



In front of the liver, separated from it by the false diaphragm, 

 is the pericardial cavity. Examine the heart ; note the thin-walled 

 auricle and the thicker walled ventricle. The auricle receives 

 blood from the body through the venous sinus which passes to 

 the ventricle, then through the arterial bulb to the gills, thence 

 to the body ; the blood is usually red. 



The pectoral fins represent the anterior limbs of other verte- 

 brates. They arise from the pectoral arch, which, in some cases, 

 is a simple cartilaginous arch, in others composed of the clavicle, 

 supraclavicle and post-temporal bones. The ventral tins repre- 

 sent posterior limbs. 



Cut down to the ribs by the side of the dorsal fin and dissect 

 away the flesh, studying the relation of the fin to the vertebral 

 column. This, perhaps, can be done more easily in a fish that 

 has been cooked, and in this way the flesh may be removed from 

 the backbone so that it may be studied more satisfactorily. 

 Study a vertebra. Notice the form of the body, the dorsal spine 

 and neural arch and the haemal spine and arch below, and note 

 the neural canal with the spinal cord, and the haemal canal with 

 its contained blood vessels. 



Open the cranial cavity and at least a portion of the spinal 

 canal, and, beginning at the front, notice the olfactory lobes giv- 

 ing rise to the olfactory nerves, then the cerebral hemispheres, 

 then the optic lobes, the widest part of the brain, then the cere- 

 bellum, and the medulla oblongata, merging gradually into the 

 spinal cord. 



Cut away the lower jaw, and, working from the mouth, dissect 



