" Existing," continuos Professor Owen, "as both the Herbivorous and Carnivorous !atm do, under such peculiar circumstances—as air-breathing animal, constantly dwelling In an element the access of which to the lungs would be immediately fatal—it might be supposed that the mechanism of the larynx, or entry to the air-passage, would be similarly modified in all the species, in order to meet the contin gencies of their aquatic existence. But we can an little predicate a community of organisation in the structure of this part, as of the circulating or digestive system In the Let area of Cnvicr. The Dugong and the Dolphin present, in fact, the two extremes in tho Manuni fermis chum, in the development of the epiglottis, which Is one of the chief internal characteristics of that class. In the true Cancels and the Delphinithr in particular, It Is remarkable for its great length, and In the Dugong it can hardly be said to exist at all." Professor Owen, after giving a minute and accurate account of the larynx, thus proceeds :— "Amongst the true CeMeta, we have observed that it is those which subsist on the lowest organised animal substance, as the Balamithr, which approach the nearest to the herbivorous species, in having the additional complexity of the =cum ; and it is interesting to find that the same affinity is manifested in the structure of the larynx. The epiglottis and arytenoid cartilages, for example, are relatively shorter in the Balmnoptera than in hdehinus; and as Mr. Hunter has observed, they arc connected together by the membranes of the larynx only at their base; and not wrapped together or surrounded by that membrane as far as the apices, as in the Dolphins. In the BaRrnoptera also, the apices of these cartilages are not expanded, as in the Dolphins, but diminished to an obtuse extremity. These points of resemblance to the condition of the larynx in the Dugong and Manatee are carried still further in the Mysticcte Whale, at least in the foetus dissected by me, and in which both the epiglottis and arytenoid cartilages were relatively much shorter, and the thyroid cartilage larger and more convex than in the Piked Whale (Bahnolstera). The thyroid cartilage is however a single piece in both genera of Balcanithr, though deeply notched above and below; and the larynx presents several interesting individual peculiarities, which however the minute and accurate descriptions and illustrations of this organ, in both the Bulamoptera and Baleen, published by Professor G. Sandifort, preclude the necessity of further dwelling upon." The diaphragm, lungs, bronchi, and trachea present in the Zoopha gous Cetaceans secondary modifications only, but important differeumss are exhibited in the nostrils, which serve to conduct the air from the atmosphere to the lungs. The necessity for the act of spouting seem', to have led to the obliteration of the organ of smelling, and to the formation of a new organ especially destined to fulfil that act. Although this organ has only been studied thoroughly in the Dolphins, the probability is, that the apparatus in all the Zoophagous Cetaceans is the same.
If, says Baron Cuvier, we trace the (esophagus upwards, we find that when it arrives opposite the pharynx it appears to divide into two passages, one of which is continued onwards to the mouth, while the other ascends to the nose. Mucous glands and fleshy fibres, which constitute several muscles, surround the last-mentioned passage. Some of these are longitudinal, and arise from the circumference of the posterior orifice of the bony nostrils, and descend along that canal to the pharynx and its sides; the others, which are annular, appear to be a continuation of the proper muscles of the pharynx. The larynx rises into this passage in a pyramidal form, and the annular fibres have the power of constricting it. Mucous follicles, which pour out their secretion by conspicuous excretory orifices, prevail in this part. When the lining of the nasal passage has reached the vomer, it becomes of a peculiar texture, thin, smooth, and black, is apparently destitute of vessels and nerves, and very dry. A fleshy valve closes the two bony nasal canals at the upper or external orifice. It is formed of two semicircles attached to the anterior edge of that orifice, which it shuts by the agency of a very strong muscle lodged above the intermaxillary bones. To open it, there is a necessity
for some foreign body to press against it from below ; and when it is closed, it debars all communication between the nasal passages and the cavities above them, which cavities are two largo membranous pouches formed by dark mucous skin, and very much wrinkled when empty; but when distended, they become of an oval shape, which in the Porpesso is about as large as a common wine-glass. These two pouches lie 'beneath tho integument in front of the nostrils, and communicate with an intermediate space immediately above those nasal organs, whose external orifice is a transverse semilunar slit. Strong fleshy fibres expand and cover the whole upper surface of this apparatus, radiating from the entire circumference of the cranium, uniting above the two pouches, and adapted for compressing them forcibly. Now we will suppose that the Cetacean has taken into its mouth water which it wishes to eject: it first sets the tongue and jaws in motion as if it were about to mallow the water ; but shutting its pharynx, it forces the water to ascend into the nasal passages, where the annular fibres above mentioned accelerate its progreas till it raises the valves and distends the membranous pouches above. The water, when once in the pouches, can be there retained till the animal wishes to spout. When that wish is present, the Cetacean closes the valve, and so prevents the descent of the water into the nasal passages, and forcibly compresses the pouches by means of the muscular expansion which overspreads them. The water, compelled then to escape by the narrow semilunar aperture, is projected to a height which corresponds to the amount of the pressure applied.
In the case of the Spermaceti Whale, it appears that the animal occupies about a seventh of its time in breathing ; and when it rises after long intervals, an enormous column of air must rush into the lungs and aerate a vast quantity of blood for the reservoir described by Hunter. In ordinary mammals, man and the quadrupeds; for instance, respiration is momentarily going on, and enough air only is inhaled to oxygenate the blood requisite for a few pulsations.
The spout-hole is simple in the Dolphins, and situated, as seen in the cut, towards the top of the head : the same simplicity exists in that of the Cachalots, but it is situated at the upper extremity of the snout. In the Whalebone Whales it is double, opening towards the summit of the head, as in the Dolphins, in a crescentic form whose convexity is sometimes anterior and sometimes posterior.
Uropoietic System.—Professor Owen observes, that if we were acquainted with the structure of the urinary organs of the Herbivorous Cetacea, as it is exemplified in the Dugong alone, we should have to establish as marked a distinction in this respect between them and the true Cetacea as in the preceding organic systems. Instead of the numerous and minute lobuli or renules'into which the kidney is sub divided in the Dolphins and Whales, it presents in the Dugong a simple compact form with an unbroken external surface ; the tubuli uriniferi terminate upon two lateral series of eleven mammillw, which project into a single elongated cavity or pelvis, from which the ureter is continued. In the Northern Manatee however, Steller, whose accuracy Professor Owen justly notices, describes the kidney as being subdivided like that of the Seal and Sea-Otter. A similar lobulated structure is also ascribed by John Hunter, in his paper on Whales, in g Phil. Trans.' (1787), to the Manatee, including it, with the Seal and White Bear, among the animals occasionally inhabiting the water. Daubenton, in his anatomical description of the Manatua A mericanus, merely notices the kidneys as oblong, and placed opposite to each other ; nor does his figure give any indication of lobulated structure ; neither does Sir Everard Home mention such structure in his Anatomy of the Manatee in 'PhiL Trans.' (1821). This want of uniformity in the structure of the kidney in the Herbivorous Cetacca is however, Professor Owen adds, of less moment with reference to their natural affinities ; since in the Pachyderms we find some species, as the Rhinoceros, and thougli in a less degree, the Elephant, presenting a subdivided kidney ; while others, as the Tapir and Hog, have it entire.