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Show 200 PROF. T. H. HUXLEY ON MENOBRANCHUS. [Mar. 17, chondrifications of the capsule of the olfactory sac, like those which certainly take place in the case of the eye and of the ear, and that the appearance of outgrowth from the trabeculae is simply due to the fact that this independent process of chondrification begins in contiguity with the trabecula and extends outwards, I do not know that there is any means of deciding the question at present. No doubt the perfect independence of the sclerotic and of the wall of the primitive auditory sac, lends countenance to the hypothesis that the olfactory sacs are provided with similar proper walls. And it is easy to imagine that the antorbital process and the ethmoidal alae* taken together, may represent the sclerotic and the periotic cartilages; but it is very difficult to find proof of the fact, and, until such proof is produced, it may be better to enumerate the auditory capsules, alone, among the paraneural elements of the skull. II. The Heart. The heart of Menobranchus has been described by Mayer and by Van der Hoeven in the works already cited. According to the former writer (I. c. p. 83), " The heart is shaped like that of Proteus anguinus, and lies free in the pericardium. It consists of a ventricle and an auricle with two appendices (Herzohren), one on each side. The truncus arteriosus arises, as in the Batrachians, from the right corner of the ventricle. Upon each side, a saccus venosus appears beneath the appendix of the auricle of its side, and receives the corresponding superior vena cava. But in the pericardial chamber there are two inferior cavae, formed by the division of the main trunk, which enters the pericardium at the upper edge of the liver. The right saccus venosus finally opens into the left; and out of this an aperture leads into the simple auricle, which, however, as has been said, presents two appendices. "Near the sinu-auricular aperlure the auriculo-ventricular opening (ostium venosum) leads into the ventricle. There are two auriculo-ventricular valves, with an interposed cleft. The ventricle is simple, but partially divided above by a median projection of its fleshy wall. The bulbus aorta gives off two branches on each side ; these pass towards the branchial arches ; and the posterior again divides. The three branchial arteries thus produced run along the anterior edges of the branchial arches to the branchial plumes; from these the branchial veins pass along the posterior edges of the branchial arches, and, after uniting into a single trunk on each side, give rise to the aorta descendens. The existence of an anastomosis between the trunks of the artery and that of the vein of each branchia was indistinct; but small branches went to the branchial filaments. "The pulmonary arteries arise from the trunk into which the branchial veins unite on each side. The pulmonary veins open, on each side, into the corresponding inferior vena cava. In addition, I found, but only on the left side, that a vein arose from the posterior vesicular end of the lung, which, uniting with a superior ovarian vein, passed directly into the vena cava inferior, as Rusconi has represented |
