An Account of the Heart and Associated Vessels in some Genera of Apoda (Amphibia)
- 1The heart and vascular arches of Ichthyophis, Ureotyphlus, Gegenophis, Scolecomorphus, Boulengerula, Dermophis and Herpele have been described and compared with those of Hypogeophis, Siphonops and Chthonerpeton. In the first six genera, there are two systemico-carotid arches which give rise cranially to the right and left systemics. The two systemic arches unite to form the dorsal aorta. In all six genera there are paired pulmonary arteries, except in Gegenophis, where there is only one which is on the right side. In Herpele the truncus gives off a right systemic and a large carotid arch, and from the cranial end of the latter there is a branch (lateral dorsal aorta) connecting it with the right systemic arch; a small pulmonary is given off before this union. The conus has a double (Ichthyophis, Dermophis, Herpele) or a single (Ureotyphlus, Gegenophis, Boulengerula, Scolecomorphus) row of valves. The truncus usually shows a septal-fold described as the “spiral-fold” in Hypogeophis and Ichthyophis, but a spiral valve is absent in the conus.
- 2The musculature of the heart is continuous throughout, there being no nodal tissue in the sinus, or at the junction of sinus and atria, atria and ventricle or ventricle and conus. In this the Apoda resemble Salamandra. However, the basket-work nature of the muscle observed in the sinus and atria of Salamandra is not seen in Apoda; the circular musculature at the S-A opening is also not developed in Apoda, the S-A valve being formed by the walls of atrium and sinus in that region.
- 3There is a large sinus ganglion only (corresponding to Remak's ganglion of the frog) and those corresponding to the atrio-ventricular ganglion of the Salamander (or Bidder's ganglion of the frog) and the bulbus ganglion of Salamandra are not found in Apoda. A few scattered nerve cells are seen in the fenestrated inter-auricular septum as in the Salamander; thus both in Apoda and Salamandra, a ganglion corresponding to Ludwig's is absent.
- 4The inter-auricular septum is fenestrated and is connected caudally with the membranous bicuspid valves as in Urodela. The musculature of the septum is continuous with that of the atrium.
- 5The A-V ring and A-V funnel are comparable, point for point, with those of the Salamander; the A-V ring is sphincter-like and the muscle fibres of the funnel are connected anteriorly with those of the ventricle and posteriorly with the papillary muscle fibres.
- 6A scheme of the circulation of the blood is described. In Ichthyophis, Ureotyphlus and Boulengerula (probably Siphonops also) the cavity is divided into lateral chambers by a dorsoventral septum in the truncus and into dorsal and ventral chambers by a lateral septum in Dermophis, since the left lateral, or dorsal, chamber, as the case may be, divides cranially into left systemico-carotid and pulmonary arches, these will convey venous blood. The right systemico-carotid and pulmonary arches, arising from right lateral or ventral portion of the truncus, will contain arterial blood. This finding is opposed to that of Acolat (1939), who said that in Ichthyophis the slight twist of the “spiral-fold” in the truncus made the venous blood flow into the pulmonary arches which arise dorsally. In Gegenophis the pulmonary artery arises as a dorsal trunk on the left, while the two systemico-carotids are given off from a larger ventral chamber of the truncus; the pulmonary artery takes venous blood to the lungs. In Herpele, where the truncus is divided into right and left lateral portions, the systemic and pulmonary arteries arising from the right side of the truncus will carry arterial blood, while the carotids contain venous blood; there is, however, a connecting vessel between the right carotid and the systemic arch.
- 7The study of the developmental stages of Ichthyophis shows that in both embryos and larvæ three vascular arches only, the third, fourth and fifth entering the external gills as afferent branchials are present; Sarasins described these as third, fourth and sixth visceral arches. The third disappears, the fourth forms the systemico-carotid and the fifth the pulmonary artery. These changes are shown diagrammatically.