vertebral column along which it passes, as the aorta descendens, to the tail, where it ends as arteria coccygea.

Each brachio-cephalic artery divides and subdivides thusa. Truncus caroticus, further separating into

a. Arteria vertebralis, ascending the neck, running through the transverse foramina of the cervical vertebræ (SKELETON, pp. 852, 853), and anastomosing in the head with the cephalic branches of the CAROTIDS (p. 76);

B. Arteria carotis communis, subdivided into the car. externa or facialis, and car. interna or cerebralis ;

b. The Arteria subclavia also separating into

a. The sterno-clavicular and thoracic arteries;

B. The axillary artery, subdivided into the scapular, humeral and brachial—the last being composed of the a. ulnaris and a. radialis, or principal arteries of the forearm and manus. The aorta descendens gives off in succession

A variable number of small vessels to the ESOPHAGUS, and intercostal vessels, generally in pairs, to the RIBS and their muscles, as well as the strong unpaired coeliac artery for the STOMACH, SPLEEN, LIVER and duodenum (pp. 141, 142) beside an a. mesenterica superior, also unpaired, supplying most of the small intestine. To them follow the right and left principal renal arteries, and those for the REPRODUCTIVE ORGANS, while a pair of crural arteries each penetrating the first lobe of the KIDNEY and, after sending a branch (a. pelvica) in the PELVIS and some of its viscera, leaving that bone in front of the ilio-pubic spine, arę continued as femoral arteries, running along the crural vein on the posterior side of the thigh and supplying chiefly the extensor muscles. Next to them come a pair of ischiadic arteries, each running ventrally past the kidneys and sending branches into their middle and lower lobes, as well as to part of the oviduct, after which it leaves the pelvis together with the ischiadic nerve through the ischiadic foramen and ultimately descends the leg, separating into the anterior and posterior tibial arteries. Lastly there are a pair of arteriæ pudendæ communes, branches of which supply the lateriventral muscles of the tail, the CLOACA and copulatory organs, and near the place where this pair originate arises also the unpaired a. mesenterica inferior, which supplies most of the rectum, part of the CÆCA and part of the cloacal region-a peculiar branch, the a. coccygo-mesenterica, being directly connected with a branch of the superior mesenteric artery.

ii. Venous. It has been already stated (p. 414) that the venous blood is collected and conveyed to the right atrium of the heart by 3 great trunks. These are composed as follows:

Each vena cava superior consists of (1) a vena jugularis which, running subcutaneously along the trachea and oesophagus, collects

DIAGRAM OF A BIRD'S VASCULAR SYSTEM. VENTRAL ASPECT.

The two halves of the Heart are drawn as if separate to shew the complete double circulation. L.A. and L.V. Left Atrium and Ventricle; R.A. and R. V. Right Atrium and Ventricle. The Arteries, except the Pulmonary (a. pulm.) which is dotted, are shaded: aaa, arcus

the blood from the head and neck; (2) a vena vertebralis which drains the brain, anastomoses by numerous and wide branches with the cephalic portions of the jugulars and, being lodged in the transverse foramina of the cervical vertebræ, which it also drains, runs along the neck; and (3) a vena subclavia which receives the blood from the thorax, beside a vena humeralis, v. radialis and v. ulnaris, combining to form the v. brachialis, and this again unites with the subcutaneous ulnar vein of the wing as the v. axillaris.

The vena cava inferior receives the blood from all the rest of the body with its viscera, entering the heart as an unpaired trunk, and close to it receiving the pair of wv. hepaticæ magnæ which carry the blood from the liver, while the rest of the venous trunk is known as the vena cava posterior, and is formed by the two vv. iliacæ communes, each of which is composed of a v. cruralis or iliaca externa and a v. hypogastrica or iliaca interna. The former of these carries the blood from the hind limb through the v. tibialis antica and v. tibialis postica, as well as through a v. femoralis, while it also receives an epigastric vein from the walls of the abdomen and its AIR-SACS (p. 4). Immediately after the v. iliac. externa has entered the pelvis, near the pectineal process (pp. 861, 862) it is joined by the v. iliac. interna, which drains the blood from the tail, vv. coccygeæ, from the pelvis and most of the viscera therein embedded, including the kidneys. Much of the venous blood is however conveyed directly into the vena iliaca communes, and numerous veins, very variable, send blood from the generative glands, from the suprarenal capsules and from the liver into the v. cava posterior.

The Hepatic Portal System remains to be mentioned. A Bird's liver receives nearly all the blood from the stomach, gut, pancreas and spleen, as well as from the liver itself. This blood enters the right hepatic lobe by a v. portalis dextra, composed of the mesenteric and coccygeo-mesenteric veins, and those from the pancreas, duodenum, proventriculus and spleen; while the left lobe receives the v. portalis sinistra with blood from the stomach. Having entered the liver, both portal veins break up into innumerable small vessels which combine again within this organ, and leave it as the vv. hepatica magnæ, which, as stated before, join the v. cava posterior, the

ascendens Aortæ; a.brc. Art. brachialis; a.desc. Aorta descendens; 4.f. Art. femoralis; A.sub. Art. subclavia; A.v. Art. vertebralis; C.c. Carotis communis; C.e. Carot. externa; C.i. Carot. interna; c.ms. Vena coccygomesentrica; coel. Art. cœliaca; er. Vena cruralis; cut.abd. Vena cutanea abdominalis; cut.uln. V. cut. ulnaris; gast. Art. gastralis; hp. Art. hepatica; hyp. Ven. hypogastrica; il. Art. iliaca; il.ex. Vena iliaca externa; il.int. V. il. interna; isch. Art. ischiadica; Jug.d. V. jugularis dextra; Jug.s. V. jug. sinistra ; ms.i. Art. mesenterica inferior; ms.s. Art. mesent. superior; r. renal arteries and veins; rad. Art. radialis; tib.a. Art. tibialis antica; tib.p. Art. tib. postica; thor. Art. thoracica; Tr.aort. truncus Aortæ; uln. Art. ulnaris; V.Br. Vena brachialis; V.c.i., v.c.p., v.c.s. Vena cava inferior, posterior and sinistra ; v.f. Vena femoralis; V.H. V. hepatica; .il.c. V. iliaca communis; v.pulm. V. pulmonaria; V.sub. V. subclavia; V.v. V. vertebralis.

combined trunk being then known as the v. cava inferior. But the left v. hepatica magna receives also the v. umbilicalis, a long unpaired vein arising in adult birds from the walls of the abdomen and its air-sacs, and frequently anastomosing with the epigastric veins. Its

Left Liver lobe

sin.

stem runs nearly midway along the visceral surface of the abdominal wall, passing first to the right of the stomach and then between the two lobes of the liver, finally joining the left hepatic vein. This peculiar vessel is .port. the remnant of one which played an important part in the embryo, for it originally collected all the blood of the yolk-sac (p. 211) into one stem which passed along the left side of the gut; and, after receiving the mesenteric vein, entered the right auricle of the heart as the v. omphalomesaraica. This stem, however, soon became surrounded by the liver, and began to form the Hepatic Portal System by partly breaking up into capillaries, while the mesenteric developed more and more, until the primitive vessel persists only as the umbilical vein.

v. port. umbilical
dext.

vein

v.mesent.

hypogastr. sinistra

DIAGRAM OF A BIRD'S PORTAL VENOUS
SYSTEM. Ventral Aspect.

Owing to the numerous anastomoses set up by veins on the confines of their several districts, some of these connexions are often used by the blood as "short cuts," and then become wider channels, while the original vessels suffer atrophy, so that quite new modifications are brought about. Such variations are so common, especially in the cervical and pelvic regions, that they deprive the Venous System of much of its taxonomic value.1

B. Lymphatic System.

The Lacteal or Absorbent vessels arise in the villi of the intestine, whence they convey the chyle into the Lymphatics (p. 139), together with the white blood or lymph corpuscles (p. 43), which are produced in the follicles at the base of the villi

1 A careful, minute and amply illustrated description of the venous system of numerous birds-"Systema venosum Avium cum eo Mammalium et inprimis Hominis collatum"-was published by Neugebauer in 1844 (Nov. Act. L.-C. Acad. xxi. pp. 517-698, tabb. xxxvi.-1.).

(p. 139, Fig. 1, L.). Lymphatics and lacteals unite, and generally follow the course of the bigger arteries and veins, often surrounding them with anastomosing network. The lymph vessels of the tail and hinder parts of the body enter the hypogastric veins, and at the point of junction a small contractile "lymph-heart" is regularly developed in the embryo and persists in many forms until maturity. The lymphatic vessels of the trunk and intestines chiefly accompany the aorta descendens and the mesenteric and coeliac arteries, finally opening into the two superior vena cavæ, as also do the branches of the lymphatic stems that come down from the head and neck, accompanying the jugular veins into which they partly enter.

VAS DEFERENS, see REPRODUCTIVE ORGANS (p. 784 and fig. p. 782).

VEERY, a name in North America (Nuttall, Man. Orn. i. p. 349) for what is otherwise known as Wilson's THRUSH, Turdus fuscescens.

VEIN (adj. venous). Veins are the vessels through which the blood flows into the HEART, no matter if this blood be venous, or arterial like that which returns purified from the LUNGS through the pulmonary veins. The walls of the veins are thinner than those of the ARTERIES, and, especially toward the extremities, contain numerous valves to hinder the reflux of the blood. Similar veins guard the entrance to the heart, but there are none in the jugular, trunk and cutaneous veins (see p. 1008).

VERTEBRÆ, see SKELETON (p. 848).

VIREOSYLVIA. (After Swainson.)

VIREO, the name of a genus proposed by Vieillot in 1807, and long since used as English, for some North-American birds, sometimes called GREENLETS. With some allied genera they seem to form a small but recognizable Family, very characteristic of the "Columbian" Fauna. Fauna. They are mostly inconspicuous in their olive-green plumage, but like the Alaudidæ (LARK) are instructive to the taxonomer, teaching him not to depend on the number of primary quills, and also shewing a considerable amount of differentiation of form within certain limits, though some of the species are not easily distinguished. By most systematists they are supposed to be allied to the Laniida (SHRIKE), and by some are even included in that Family, but on grounds that are at least debatable. Baird in 1866 (Rev. Am. B. pp. 321-400) insisted forcibly on the distinctness of the Vireonida, to which he assigned 7 genera and some subgenera, being therein followed in 1873 by Messrs. Sclater and Salvin (Nomencl. Av. pp. 11-13); but Sundevall in 1872 (Tentamen, p. 13) had