Bibliography of the Heart.
(492) A. C. Bernays. “Entwicklungsgeschichte d. Atrioventricularklappen.” Morphol. Jahrbuch, Vol. II. 1876.
(493) E. Gasser. “Ueber d. Entstehung d. Herzens beim Hühn.” Archiv f. mikr. Anat., Vol. XIV.
(494) A. Thomson. “On the development of the vascular system of the fœtus of Vertebrated Animals.” Edinb. New Phil. Journal, Vol. IX. 1830 and 1831.
(495) M. Tonge. “Observations on the development of the semilunar valves of the aorta and pulmonary artery of the heart of the Chick.” Phil. Trans. CLIX. 1869.
Vide also Von Baer ([291]), Rathke ([300]), Hensen ([182]), Kölliker ([298]), Götte ([296]), and Balfour ([292]).
Arterial System.
In the embryos of Vertebrata the arterial system consists of a forward continuation of the truncus arteriosus, on the ventral side of the throat ([figs. 363], abr, and [364], a), which, with a few exceptions to be noticed below, divides into as many branches on each side as there are visceral arches. These branches, after traversing the visceral arches, unite on the dorsal side of the throat into a common trunk on each side. This trunk ([figs. 363] and [364]) after giving off one (or more) vessels to the head (c´ and c) turns backwards, and bends in towards the middle line, close to its fellow, immediately below the notochord ([figs. 21] and [116]) and runs backwards in this situation towards the end of the tail. The two parallel trunks below the notochord fuse very early into a single trunk, the dorsal aorta ([figs. 363], ad, and [364], a´´). There is given off from each collecting trunk from the visceral arches, or from the commencement of the dorsal aorta, a subclavian artery to each of the anterior limbs; from near the anterior end of the dorsal aorta a vitelline artery (or before the dorsal aortæ have united a pair of arteries [fig. 125], R of A and L of A) to the yolk-sack, which subsequently becomes the main visceral artery[227]; and from the dorsal aorta opposite the hind limbs one (or two) arteries on each side—the iliac arteries—to the hind limbs; from these arteries the allantoic arteries are given off in the higher types, which remain as the hypogastric arteries after the disappearance of the allantois.
Fig. 363. Diagrammatic view of the head of an embryo Teleostean, with the primitive vascular trunks. (From Gegenbaur.)
a. auricle; v. ventricle; abr. branchial artery; c´. carotid; ad. dorsal aorta; s. branchial clefts; sv. sinus venosus; dc. ductus Cuvieri; n. nasal pit.
The primitive arrangement of the arterial trunks is with a few modifications retained in Fishes. With the development of the gills the vessels to the arches become divided into two parts connected by a capillary system in the gill folds, viz. into the branchial arteries bringing the blood to the gills from the truncus arteriosus, and the branchial veins transporting it to the dorsal aorta. The branchial vessels to those arches which do not bear gills, either wholly or partially atrophy; thus in Elasmobranchii the mandibular trunk, which is fully developed in the embryo ([fig. 193], 1av), atrophies, except for a small remnant bringing blood to the rudimentary gill of the spiracle from the branchial vein of the hyoid arch. In Ganoids the mandibular artery atrophies, but the hyoid is usually preserved. In Teleostei both mandibular[228] and hyoid arteries are absent in the adult, except that there is usually left a rudiment of the hyoid, supplying the pseudobranch, which is similar to the rudiment of the mandibular artery in Elasmobranchii. In Dipnoi the mandibular artery atrophies, but the hyoid is sometimes preserved (Protopterus), and sometimes lost.
In Fishes provided with a well developed air-bladder this organ receives arteries, which arise sometimes from the dorsal aorta, sometimes from the cæliac arteries, and sometimes from the dorsal section of the last (fourth) branchial trunk. The latter origin is found in Polypterus and Amia, and seems to have been inherited by the Dipnoi where the air-bladder forms a true lung.
The pulmonary artery of all the air-breathing Vertebrata is derived from the pulmonary artery of the Dipnoi.