682 



CETOLOG 



I-tfynx. 











Blow- 

 holes. 

 PLATE 

 CXXXIII. 

 Fig. 8, 9. 



that of quadrupeds ; and that they therefore possess 

 a similar system of circulating and respiratory or- 

 gans. 



SECT. V. Respiration. 



The structure and physiology of the respiratory 

 organs in cetaceous animals, deserve particular atten- 

 tion, as they exhibit peculiarities not to be found in 

 any other class'of animals, and are in themselves suf- 

 ficient to distinguish the cetacea from the mammalia. 

 Many of the amphibious quadrupeds, especially the 

 manati, have fins resembling those of the cetacea, but 

 none of them possess the peculiar larynx and spout 

 holes of the latter. 



The larynx consists of the same number of carti- 

 lages with that of quadrupeds, but their appearance 

 and articulation are somtwhat different. In some 

 species, as the porpesse and piked whale, the os hyoides 

 consists but of one piece, while in the dolphin, or 

 bottle-nosed whale, it is composed of three pieces, 

 besides two additional cartilages attached to it from 

 above. This bone has no attachment to the head by 

 means of other bones, as is the case in many quadru- 

 peds. The thyroid cartilage differs in figure in the 

 several species, but in general it is broader laterally, 

 than from the atlantalto the sacral edge (from above 

 downward). The cricoid cartilage is broad and flat, 

 and deeper laterally and on its dorsal part, than on 

 its sternal side. It is extremely thick and strong. The 

 two arytenoid cartilages project considerably, and are 

 united to each other almost to their extremities. The 

 epiglottis is sometimes not attached to the aryte- 

 >ioids, while in others it is so united to them, as to 

 form with them a complete canal, terminating in the 

 glottis. In this latter case, the passage through the 

 glottis is very much contracted, but below this con- 

 traction the trachea swells out into a tube of consi- 

 derable size. From this peculiar structure, Mr Hun- 

 ter was of opinion that these animals possess no voice ; 

 though we are assured by many observers, 'that they 

 emit sounds resembling a sort of dull bellowing or 

 lowing. 



The lungs have little peculiar, except that they are 

 long and thin, and closely attached both to the pleura 

 and the diaphragm. They are also not divided into 

 lobes, as in man and quadrupeds, and are of a firmer 

 texture. 



m. The diaphragm is attached at its sternal edge to 

 the abdominal muscles, whence it passes obliquely 

 backwards, and is inserted into the spine much more 

 sacrad or lower than in quadrupeds. This muscle, 

 and all those parts concerned in inspiration, are, in 

 the cetacea, exceedingly strong. 



There is something peculiar in the structure of the 

 thorax, which is not entirely surrounded by the ribs ; 

 hence its cavity is less easily enlarged. This defect 

 is supplied chiefly by the greater proportional strength 

 in the diaphragm, which is hence supposed to be the 

 principal organ of inspiration. 



What are called the spout holes or blorv holes, are 

 two canals situated near the middle of the arch form- 

 ed by the bones of the cranium, a little behind that 

 part where rises the protuberance in which they ter- 

 minate by the external orifices. They proceed from 

 the back of the mouth, and after traversing in a cur- 

 ved direction the interior of the skull, open externally 



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* 



*** 



in some part of its upper surface. In most species Cetolop 

 the bony canal is double, and in some the two parts ^-^ "V 

 eontinue distinct as far as the external opening ; this 

 is the case in the balsenae. In most, however, the 

 two canals unite near the top of the head, and termi- 

 nate by a single external orifice. This ^rifice differs 

 both in form and situation in the several tribes. In 

 the porpesse, grampus, spermaceti whale, and some 

 others, the orifice is transverse ; in the balaence it is 

 longitudinal. It is always situated on that part of 

 the head which is most protuberant. In some tribes 

 this part is near the forehead, in others near the mid- 

 dle of the head. In some, as the balsena and physc- 

 ter tribes, its course through the cranium is straight ; 

 in others, as the narwhals and dolphins, it is curvi- 

 lineal. 



The most curious part of the mechanism of the 

 blow holes remains to be described, viz. the connec- 

 tion between the bony parts of these passages, and 

 the contiguous membranes and muscles. We have 

 already seen, that the eustachian tube ascends to- 

 wards the top of the nostrils, and have noticed the 

 cavity or empty space on its internal surface. With 

 this hole are connected several membranous cavities 

 or sinuses, and this compound cavity communicates 

 with the frontal sinuses, by a canal which ascends 

 forwards towards the orbit ; but the sinuses have no 

 immediate communication with the nostrils properly 

 so called. 



On examining the gullet in these animals, we find 

 that when it reaches the top of the larynx, it seems 

 to divide into two tubes, one of which is continued into 

 the mouth, while the other ascends towards the nose*. 

 This latter is surrounded with glands and fleshy fi- 

 bres, that form several muscles. Some of these fibres 

 are longitudinal, and are attached round the posterior 

 orifice of the bony part of the nostrils or blow holes, 

 and descend along the tube as far as the pharynx, 

 and down the sides of this cavity ; the other fibres 

 are annular, and appear to be a continuation of the 

 proper muscle of the pharynx. Now, as the larynx 

 rises into this canal like a pyramid, these annular fi- 

 bres are able to compress it by their contractions. 

 The two bony canals near their upper or external ori- 

 fice are closed by a fleshy valve, in the form of two se- 

 micircles attached to the anterior border of the orifice, 

 which the valve closes by means of a very strong 

 muscle, inserted into the upper surface of the inter- 

 maxillary bones. To open the orifice, requires a strong 

 effort from below upwards. When this valve is clo- 

 sed, it intercepts all communication between the blow 

 holes and certain cavities placed above the valve. 



These cavities are two large membranous bags, 

 formed of a blackish mucous skin, which are much, 

 wrinkled when empty, but when inflated assume an 

 oval form, and are of considerable capacity. These 

 two bags are concealed below the skin, in the fore- 

 part of the blow holes. They both open into an in- 

 termediate cavity, placed immediately in the blow 

 holes, and communicating with the external air by a 

 narrow circular chink. There is an expansion of 

 very strong fleshy fibres, which covers the whole of 

 this apparatus, proceeding in a radiating form by the 

 neighbouring parts of the cranium, and uniting over 

 the two bags, so as to be capable of compressing 

 these with great force. 

 Such is the mechanism of the blow holes as descri- 



