VASCULAR SYSTEM OF THE FROG 1 



1. Secure a specimen, with the blood vessels injected, and fasten it 

 ventral surface up in a dissecting pan. Expose the heart and identify 

 the major divisions (auricles, ventricle, sinus venosus, conus ar- 

 teriosus). Trace the conus arteriosus leading from the ventricle and 

 note that, just anterior to the auricles of the heart, it divides into two 

 branches from each of which three arteries arise. Identify these arteries 

 arising from the right branch of the conus arteriosus as follows: (a) the 

 pulmocutaneous artery, which arises nearest the heart and runs to the 

 skin and lungs ; (6) the systemic arch which runs laterally and dorsally 

 and unites with the left systemic arch to form the large (c) dorsal aorta 

 noted in paragraph 2 below; (d) the common carotid artery which 

 shortly branches to form (e) an internal carotid and (/) an external 

 carotid. These vessels supply the entire head region with arterial blood. 



2. Note the location of these same arteries as they arise from the left 

 branch of the conus arteriosus, and then trace the right and left systemic 

 arches laterally and dorsally to where they unite, posterior to the heart 

 and close to the dorsal body wall, to form the dorsal aorta. Just pre- 

 vious to their union each systemic arch gives rise to (a) the occipito- 

 vertebral artery which runs to the jaws, nasal region, and vertebral 

 column and (6) to the brachial artery running to the fore limbs and 

 nearby body wall. 



3. Trace the dorsal aorta posteriorly, noting a number of important 

 branches which supply the alimentary canal and associated structures, 

 urogenital system and nearby body wall. Trace the aorta to the posterior 

 part of the abdominal cavity and note its division into the right and left 

 iliac arteries which, after branching to form several small vessels, con- 

 tinue posteriorly out of the body cavity and into each of the hind limbs. 



4. Make a drawing to show the heart and the arterial system as ob- 

 served in the previous paragraphs. 



5. It will not be profitable to trace the vessels of the venous system 

 which return the blood to the heart and which run parallel, in most cases, 

 to the vessels of the arterial system, but the complete course of the circu- 

 lation of the blood through the body should be understood and diagrammed. 



6. Observe under the microscope the circulation of the blood as seen 

 in the living interdigital web of the Frog's foot. In a favorable area note 

 (a) the larger arterial vessels, with a comparatively rapid pulsating blood 

 flow which results from the change in pressure due to the contractions 

 of the ventricle ; (b) the tiny capillaries which form a connecting link 

 between the arteries and veins. Their diameter is, in many cases, sufficient 

 only to permit the passage of (c) the red blood corpuscles in single file. 

 The capillaries in turn connect with (d) the veins which carry the blood 

 in a slow -moving, regular-flowing stream towards the heart. 



i B. pp. 192-201. 

 333 



