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The Arterial System.
I.—The Carotid Arch.
For the purpose of the following description, the detailed distribution of the vessels of the brain will not be considered. The distribution of the main vessels arising from the carotid arch in Leiopelma differs little from that already described in detail for Rana esculenta (Ecker, 1889). General characteristic differences may be summarised as follows:—
| (a) |
A slender cutaneous artery arises a short distance beyond the point of origin of the lingual or external carotid artery and passes back to supply the cutaneous capillaries of the ventral surface of the body at approximately shoulder level. (Text Figure I.) |
Text Fig. 1.—The Carotid Artery and its branches. Ventral aspect. (Tongue and mucous membrane of palate have been removed from right half of head.) a.p.—Anterior branch of palatine artery. b.p.p.—Branch of posterior palatine artery. c.a.—Carotid artery. c.ar.—Carotid arch. c.b.l.—Cutaneous branch of lingual artery. e.g.—Carotid gland. d.b.l.—Deep branch of lingual artery. i.c.—Internal carotid artery. 1.—Lingual or external carotid artery. m.m.p.—Mucous membrane of palate deflected forward. o.—Orbit. p.a.—Palatine artery. ps.—Parasphenoid. s.b.l.—Superficial branch of lingual artery. t.—Tongue. t.a—Truncus arteriosus.
| (b) |
A single palatine artery arises from the carotid artery immediately before the latter crosses the posterior border of the orbit. This palatine trunk supplies a small vessel to the underlying mucous membrane before dividing into two ultimate branches which correspond in function to the anterior and posterior palatine arteries of Rana. |
| (c) |
The anterior spinal artery communicates with the occipito-vertebral artery on each side by a single ventral or spinal branch arising from the latter. |
II.—The Systemic Arch. (Plate 43.)
From before backward, the branches arising from the left systemic arch before its junction with the right arch to form the dorsal aorta are as follows:—
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| (i) |
An oesophageal artery. |
| (ii) |
A gastric artery, passing to the stomach. |
| (iii) |
The occipito-vertebral artery, passing to the dorsal region of the body. |
| (iv) |
The subclavian artery, supplying the shoulder and arm. |
| (v) |
Three dorso-lumbar arteries, supplying the muscles of the body wall. |
| (vi) |
Three branches, passing to the oviduct, kidneys and fat-body of the same side. |
The branches of the right systemic arch are symmetrical with those of the left, except for the lack of oesophageal and gastric arteries on the right side.
The dorsal aorta gives rise to a further series of branches:
| (1) |
The coeliaco-mesenteric artery, supplying the alimentary canal and its associated glands. |
| (2) |
A variable number of urinogenital arteries, supplying the kidneys, gonads and oviducts. |
| (3) |
Several pairs of small dorso-lumbar arteries, passing to the dorsal body wall. |
| (4) |
An anterior haemorrhoidal artery, arising either before or behind the last pair of renal arteries and passing to the large intestine. |
| (5) |
A posterior haemorrhoidal artery, supplying the large intestine and the bladder. |
| (6) |
Two iliac arteries, formed by the ultimate bifurcation of the dorsal aorta and passing to the hind limbs. |
The occipito-vertebral artery, which arises opposite the level of the shoulder, passes inward and upward towards the vertebral column. Close to the latter, a small central branch comes off the main trunk and passes inward to the ventral surface of the spinal cord, where it unites with the anterior spinal artery. The main artery continues upward to the dorsal level of the vertebral column, after which it passes forward and outward as the occipital artery until it reaches the inner posterior border of the orbit. Before descending to supply the lining of the inner wall of the orbit, the occipital artery gives off two branches, one of which supplies the skin covering the outer wall of the orbital region, while the other passes downward to the roof of the mouth.
In Leiopelma, a vessel corresponding fully to the vertebral artery of Rana does not exist, and the only representative of the “rami spinales” (Ecker, 1864) of the latter is the small ventral vessel which unites with the anterior spinal artery. The functions of the vertebral artery appear to be served in Leiopelma by the dorso-lumbar arteries arising from the systemic arch and renal arteries and supplying the vertebral column and muscles surrounding it. A vertebral artery is lacking also in Hyla aurea. (Marriner, 1905.)
The subclavian artery conforms largely in its distribution to the same vessel in Rana, but exhibits minor differences in the positions of the finer branches supplying skin and muscles. Leiopelma exhibits no trace of the costo-cervical branch of the subclavian artery, but its function is carried out by means of the three pairs of dorso-
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lumbar arteries arising from the systemic arches. The latter run between the transverse processes of the second to the fifth vertebrae and pass through the intervertebral foramina to supply the vertebral canal. In addition, they feed the surrounding muscles.
An interesting feature shown in Leiopelma is the presence of three oviducal and renal arteries arising from the backwardly-curving region of each systemic arch. (Plate 42.) The two anterior branches are short vessels which pass directly outward and backward to the anterior region of the corresponding oviduct. Shortly before the dorsal aorta is formed, a third artery takes its origin. This, after branching to supply the fat-body, passes diagonally back over the antero-ventral surface of the kidney, until it reaches the outer border of this organ. It then turns backward and runs toward the posterior end of the kidney, sending out, more or less at right angles, several arteries which ramify over the surface of the corresponding oviduct.
The Dorsal Aorta.
1.—The Coeliaco-mesenteric Trunk.
The coeliaco-mesenteric trunk gives rise to the usual two branches:
| (a) |
A gastric artery. |
| (b) |
A mesenteric artery. |
The distribution of the branches arising from these main vessels is shown in Plate 41.
2.—The Urinogenital Arteries. (Plate 42.)
The arteries from the dorsal aorta to supply the kidneys and reproductive organs, although much more regularly arranged than the efferent renal veins, are rarely symmetrically placed. Most commonly, there are four pairs of urinogenital arteries, with the successive pairs comparatively widely spaced. Sometimes, the members of the two middle pairs are symmetrical, while those of the anterior and posterior pairs show variations in their positions. In other, more abnormal individuals, the arteries passing to one kidney may show no correspondence either in number or arrangement with those of the opposite side. In extreme cases two arteries have been observed on one side, and a single, large artery on the other. Where four pairs of renal arteries are present, it is generally found that each of the first two vessels on each side passes to the inner border of the corresponding kidney and divides into two, one branch passing into the substance of the kidney, while the other passes to the ovary of the same side. The third artery, in addition to supplying the kidney and the gonad, produces an extra branch which passes over the ventral surface of the kidney to carry blood to the portion of the oviduct more posterior to that supplied by the oviducal branch from the systemic arch. The fourth renal artery also sends a branch to the oviduct, but does not always supply the ovary. In the males of Leiopelma, the derivation of the spermatic arteries appears to correspond to that of the ovarian arteries.
The Iliac Arteries.
The dorsal aorta bifurcates near the middle of the urostyle to
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form the iliac arteries, each of which passes obliquely outward and backward to the base of the corresponding thigh to become continuous with the sciatic artery. The course of the latter is essentially similar to that in Rana, and peroneal and tibial arteries are formed at the knee in similar fashion. As the tibio-fibula is not perforated in Leiopelma, however, the main tibial artery curves around the bone instead of passing through it as in Rana.
III.—The Pulmo-cutaneous Arch.
Little deviation from the typical Anúran condition is seen in the vessels of the pulmo-cutaneous arch. The pulmonary artery is approximately equal in diameter to the cutaneous trunk, but the extensive plexus of cutaneous capillaries leaves little doubt as to the importance of the respiratory function of the skin, notwithstanding the semi-terrestrial habitat of Leiopelma.