Section 45. The following are the chief branches of the aorta. The student should be able to follow them with certainty in dissection; they are all displayed in the [Figure]; but it must not be imagined for a moment that familiarity with this diagram will obviate the necessity for the practical work; (in.) is the innominate artery; it forks into (s.cl.a.) the right subclavian, and (r.c.c.) the right common carotid. Each carotid splits at the angle of the jaw into an internal and an external branch. The left common carotid, (l.c.c.) arises from the base of the innominate,* (l.s.cl.a.) the left subclavian, directly from the aorta. The aorta now curves round to the dorsal middle line, and runs down as seen in Figure 1, [Sheet 1] (d.ao.) and Figure 1, [Sheet 2] (d.ao.). Small branches are given off to the ribs, and then comes the median coeliac (coe.a.) to the stomach and spleen, the median superior mesenteric (s.mes.a.) to the main portion of the intestine, and the inferior mesenteric (p.m.a.) to the rectum. Note that no veins to the inferior vena cava correspond to these arteries-- the blood they supply going back by the portal vein (p.v.). The paired renal arteries (r.a.) supply the kidneys, and the common iliacs (c.il.a.) the hind legs, splitting into the internal iliacs (i.il.a.) and the femoral (f.).
{Lines from Second Edition only.}
[The student should note that the only arteries in the middle line are those supplying the alimentary canal.]
{Lines from First Edition only.}
* -The figure is inaccurate, and represents the left common carotid as arising from the aortic arch.-
Section 46. The distribution of the veins of the rabbit has only a superficial parallelism with arteries. The chief factors of vena cava inferior are the hepatic vein (h.v.), which receives the liver blood, the renal veins (r.v.), from the kidneys, the ilaeo-lumbar, from the abdominal wall, and the external (e.il.v.) and internal ilias (i.il.v.); with the exception of the renal veins none of these run side by side with arteries. The superior cavae (r. and l.v.c.s.) are formed by the union of internal (i.j.) and external jugular (e.j.) veins with a subclavian (s.cl.v.) from the fore limb. The term pre-caval vein is sometimes used for superior cava. The attention, of the student is called to the small azygos vein (az.) running into the right vena cava superior, and forming the only asymmetrical (not-balancing) feature of the veins in front of the heart; it brings blood back from the ribs of the thorax wall, and is of interest mainly because it answers to an enormous main vessel, the right post-cardinal sinus, in fishes. There are spermatic arteries and veins (s.v. and a.) to the genital organs. All these vessels should be patiently dissected out by the student, and drawn.
Section 47. Between the final branches of the arteries and the first fine factors of the veins, and joining them, come the systemic capillaries. These smallest and ultimate ramifications of the circulation penetrate every living part of the animal, so that if we could isolate the vascular system we should have the complete form of the rabbit in a closely-meshed network. It is in the capillaries that the exchange of gases occurs and that nutritive material passes out to the tissues and katastases in from them; they are the essential factor in the circulatory system of the mammal-- veins, arteries, and heart simply exist to remove and replace their contents. The details of the branching of the pulmonary artery and the pulmonary veins need not detain us now.
Section 48. Summarising the course of the circulation, starting from the right ventricle, we have-- pulmonary artery, pulmonary capillaries, pulmonary vein, left auricle, left ventricle, aorta, arteries, and systemic capillaries. After this, from all parts except the spleen and alimentary canal, the blood returns to systemic veins, superior or inferior cavae, right auricle, and right ventricle. The blood from the stomach spleen, and intestines however, passes via {through} the portal vein to the liver capillaries and then through the hepatic vein to inferior cava, and so on. Material leaves the blood to be excreted in lungs, kidneys, by the skin (as perspiration), and elsewhere. New material enters most conspicuously;
(a) by the portal veins portal veins and
(b) by the thoracic duct and left superior cava.
Section 49. The following table summarises what we have learnt up to the present of the physiology of the Rabbit, considered as a mechanism using up food and oxygen and disengaging energy:--
-Air_ {Nitrogen... returned unchanged.}
{Oxygen... through Pulmonary Vein to--} {see 3.}
-Food_ {Carbo-Hydrates (Starch, Sugar, Cellulose.)} Sugar.
{Protein.} {Peptones.}
{Fat (little in Rabbit.)} {Glycerine, and fatty acids in soups.}
{Rejected matter got rid of in Defaecation.}
1a. {Chyle in Lacteals going via {through} Thoracic Duct and Left
Superior Cava to--} {see 2.}
1b. {Veins of Villi--}
{Portal Vein--}
{Liver--}
{Hepatic Vein and Inferior Cava to--} {see 2.}
2. {Right side of heart; then to lungs, and then to--} {see 3.}
3. {Left side of heart; whence to Systemic Arteries and Capillaries.}
4. {The tissues and -Kataboly_.}
5. {Urea (?Liver) Kidney and Sweat Glands}
{CO2} {Lungs}
{H2O} {Lungs, Kidney, Sweat Glands}
{Other Substances} {Mainly by [Kidney,] Liver and Alimentary Canal}