15 



and a large gastric artery to the cardiac limb of the stomach. The 

 anterior intestinal artery supplies the pyloric limb of the stomach, 

 the pancreas, duodenum, and right side of the large intestine. 



Small genital arteries, supplying the reproductive glands, arise 

 from the coeliac near its origin. (In Eugaleus the genital arteries 

 arise from the anterior and posterior mesenteric arteries.) 



At about the middle of the abdominal cavity two arteries arise 

 close together from the aorta. The anterior of the two is the an- 

 terior mesenteric artery; it passes to the left side of the large intes- 

 tine and its branches anastomose more or less with those of the 

 anterior intestinal artery. The posterior vessel is the lieno-gastric ; 

 it goes to the spleen, pancreas, and loop of the stomach. 



The posterior mesenteric artery leaves the aorta a little distance 

 back of the lienogastric and passes to the rectal gland, rectum, and 

 cloaca. 



Free the kidney from the body wall along its outer edge and 

 turn it up so as to expose its dorsal surface. Observe the numerous 

 parietal arteries (going to the body wall) and renal arteries (to the 

 kidney), which spring from the dorsal aorta. Branches of the 

 parietals also pass into the kidney. 



A pair of small iliac arteries pass into the pelvic fins. 



Oviducal arteries, one or several on each side, arise from the 

 aorta behind the coeliac artery and pass to the oviduct. Their size 

 varies largely with the development and physiological condition of 

 the oviduct. 



The aorta is continued in the tail as the caudal artery. 



DISSECTION OF THE HEART. Remove the heart together with the 

 ventral aorta from the body and fasten it, dorsal side up, under 

 water. Open the sinus venosus with scissors, wash it out, and ob- 

 serve the vertical slit-like opening into the auricle and the two mem- 

 braneous valves which guard it. 



Continue the cut through the sinu-auricular aperture along the 

 median dorsal line of the auricle; observe the thin walls of the 

 auricle and their strengthening by an irregular mesh of muscles, 

 the musculi pectinati; the shape and position of the auriculo-ventri- 

 cular aperture; the flaps of the auriculo-ventricular valve. Press 

 upon the sides of the ventricle and, if possible, observe the mode of 

 action of the valve. 



Cut across the ventricle from the auriculo-ventricular aperture. 

 Carry another incision from this along the dorsal side of the conus 

 arteriosus. Observe the small size of the cavity of the ventricle, the 

 thickness of its walls, and the projecting network of muscles, the 

 columnae carneae, some of which are attached to the edges of the 

 auriculo-ventricular valves. 



In the conus arteriosus observe the rows of three pocket-like 

 valves each around the proximal end (semilunar valves), and a 

 single row of three similar but larger valves at the junction of the 

 conus and ventral aorta. There is some variability in the number 

 of rows of valves in the conus of Squalus; there are always three 

 rows of three valves each in that of Eugaleus. 



In the aorta notice the apertures without valves which lead into 

 the afferent branchial vessels. 



HEPATIC PORTAL SYSTEM. The hepatic portal vein is the large 

 vein entering the liver alongside the hepatic artery and bile duct. It 

 receives branches from the stomach, pancreas, spleen, intestine, and 

 rectal gland. 



