GENERAL BIOLOGY 



opposite side to form the dorsal aorta. Trace the systemic arches 

 dorsally around the oesophagus to their point of union. The dorsal 

 aorta extends to the posterior end of the body cavity where it di- 

 vides into two branches, the right and left iliac arteries to the hind 

 legs. From each systemic arch a subclavian artery passes to the 

 front leg. Named in order, beginning with the most anterior, the 

 following branches arise from the dorsal aorta: (a) coeliaco- 

 mesenteric (to liver, stomach and intestine), (b) ovarian (or 

 spermatic) to gonads, (c) renal (to kidneys). 



(3) The posterior or pulmonary arch runs to the lungs giving 

 off on its way a large cutaneous branch which carries blood to the 

 skin for aeration when the animal is submerged. 



d. Veins (the afferent vessels). 



The blood is returned to the heart through five main trunks, 

 right and left anterior venae cavae, a median posterior vena cava, 

 and right and left pulmonary veins. The venae cavae are joined 

 together at the heart to form the sinus venosus, which opens into 

 the right auricle. 



(1) Each anterior vena cava is formed by the confluence of 

 three veins: (a) external jugular, from face and throat; (b) in- 

 ternal jugular, from cranial cavity; (c) axillary formed by union 

 of the subclavian from the arm, and the musculo-cutaneous from 

 the skin and abdominal muscles. 



(2) The posterior vena cava arises by the union of several large 

 branches coming from each kidney (renal vein) ; anteriorly it re- 

 ceives a large vein from each lobe of the liver (hepatic veins). 



The anterior-abdominal vein (unpaired) arises from the right 

 and left iliac veins from the legs and runs to the liver and heart. 



(3) Portal veins (veins arising from and ending in capillaries) : 

 Blood from the hind limbs is carried to the kidneys by the renal- 

 portal veins which enter the kidneys along their external borders. 

 The hepatic-portal vein carries blood from the stomach and in- 

 testine to the liver. 



(4) The right and left pulmonary veins open into the left 

 auricle through a common opening. 



Make a diagram of the heart and vascular trunks. 



Before leaving the laboratory open the skull and spinal canal 

 as follows : Cut the skin along the median dorsal line and reflect it. 

 With forceps pick off the muscles from the vertebrae. Open the 

 neural canal by cutting into the membrane just posterior to the 



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