877 



CETACEA. 



CETACEA. 



873 



The enormous development of the intermaxillary bones of the 

 Dugong carries up the aperture of the bony nostrils much higher than 

 in the Manatee, and it is situated at the superior part of the head in 

 the middle of its length and directed upwards, its form being a large 

 oval as in the Manatee of Senegal. The whole skull, and particularly 



Skull of Dugong (Halicore Dugong] . 



the frontal bones, are for the same reason much shorter in proportion 

 than in the Manatee. The branches of the frontal bone which form 

 the upper part of the orbit are more delicate and more rugose. The 

 maxillary portion which serves as a floor for the orbit is narrower ; 

 the jugal bone in turning to form the anterior and inferior edge of the 

 orbit is more compressed and directed more downwards. There is 

 also a lachrymal bone in the anterior angle more considerable than in 

 the Manatee, but equally without any hole. The zygomatic apophysis 

 of the temporal bone is more delicate and more compressed. The 

 connections of the bones of the cranium are the same, but at the 

 inferior surface the baailary bone is united with the lateral occipital* 

 rather than with the posterior sphenoid. A very great solution of 

 continuity is seen in the bottom of the orbit and of the temple, and 

 establishes in the skeleton an extensive communication between these 

 two fossae and that of the nostrils ; it is intercepted between the 

 maxillary, the frontal, the anterior sphenoid, and the palatine bones. 

 The continuity of the temporal portion of the palatine with the rest 

 of the bone is not here concealed, as in the Manatee, by a production 

 of the maxillary bone. The occiput is narrower and its crest less 

 marked than in the Manatee ; the frame of the tympanum is also 

 narrower and more delicate, but the bone of the ear is disposed nearly 

 in the same way, and is let in between the same bones. There also 

 remains in the skeleton a large empty space between that bone, the 

 basilary, and the anterior sphenoid. Within the cranium there is no 

 bony tentorium ; the cribriform fossa is reduced to two simple 

 depressions very much separated from each other, and which terminate 

 anteriorly by two or three small holes. There is no sella Turcica. 

 The optic aperture is a long narrow canal. The lower jaw is of a 



two long slender bones, which have some resemblance iu form to the 

 clavicles of man. There are V-shaped bones articulated under the 

 interval of the vertebra after that which comes beyond the pelvis. 

 They diminish by degrees, and seem to terminate altogether under 

 the last fourth of the tail. 



The shoulder-blade, as in the Manatee, has its anterior angle 

 rounded, the posterior angle sharp, and carried well backwards ; the 

 posterior border very oblique and slightly concave. Its spine is pro- 

 jecting, its acromion pointed, but much less elongated than in the 

 Manatee. The coracoid process is much more pointed than in that 

 animal, and directed forwards and a little inwards. The humerus is 

 much stouter and shorter than in the Manatee ; its deltoid crest pro- 

 jects more, and it forms with the great tuberosity a rhomboidal pro- 

 tuberance. The bones of the fore-arm are rather longer in proportion 

 than those of the Manatee, but their form is the same, and they are 

 equally conjoined at their two extremities. There are only four carpal 

 bones ; two of which are in the first row, one for the radius, the other 

 for the ulna ; and two in the second, the first of which supports the 

 metacarpals of the thumb and fore finger, and the second those of the 

 middle and ring-finger. That of the little finger bears upon the 

 second bone of the second row, and upon that of the first. The 

 thumb, as in the Manatee, is reduced to a pointed metacarpal. The 

 other fingers have the ordinary number of phalanges, the last of which 

 are compressed and obtuse. (' Ossemens Fossiles.') 



Professor Owen, in his ' Anatomy of the Dugong' ('Zool. Proc.,' 

 1838), remarks that after the excellent and elaborate descriptions of 

 the osteology of that animal by Cuvier, Ruppell, and others, but little 

 remains to be said on the subject. The bones, Professor Owen 

 observes, are chiefly remarkable, as in the Manatee, for their dense 

 texture and the non-development of medullary cavities in them. 

 This reptile-like condition of the skeleton is, he adds, further exempli- 

 fied in the loose connection of the bones of the head. The bones are 

 not loaded with oil as in the true Cetacea. All the specimens ex- 

 amined by the Professor presented 7 cervical and 19 costal vertebrae, 

 corresponding to the 19 pairs of ribs ; but the number of the remaining 

 | vertebrae exceeded that ascribed to the Dugong by Home and Cuvier, 

 I there being at least 30, making in all 55. Ruppell assigns to the 

 I Halicore tabernaculi 7 cervical, 19 dorsal, 3 lumbar, 3 pelvic, and 27 

 caudal vertebrae ; in all 59. Professor Owen found, as Ruppell also 

 I describes, that the first four pairs of ribs reached the sternum through 

 I the medium of cartilages ; all the others terminated freely in the mass 

 | of abdominal muscles : the tenth to the fifteenth Professor Owen found 

 the longest, and the last the shortest. 



The Professor points out that the affinity of the Dugong to the 

 Pathydermata is here again illustrated by the great number of the 

 ribs. The lower jaw is, he observes, articulated to the cranium by a 

 true synovial capsule, reflected over cartilaginous surfaces, and not, 

 as in the Carnivorous Cetacea, by a coarse and oily ligamentous sub- 

 stance. In treating of the rudimental pelvic bones of the Dugong, 

 he remarks that in the true Cetacea the parts analogous to the iachia 

 are alone present, and that those bones serve a similar purpose in 

 [ the Dugoug. 



Skeleton of Dugong (Halicore Dugong}. 



height corresponding with the curvature and length of the intermaxil- 

 lary bones. This part shows in the adult the remains of three or four 

 alveoli on each side. 



The atlas is very similar to that of the Manatee ; the axis the same. 

 The five other cervical vertebrae are very delicate, but not conjoined. 

 There are 18 dorsal vertebra, the spinous apophysea of which are 

 arranged nearly in a straight line. Counting from the ninth, the ribs 

 do not attach their head between two vertebrae, but only to the same 

 vertebra, to the transverse apophysis of which they are articulated. 

 The ribs are not nearly so stout as in the Manatee, but, notwithstanding, i 

 the first are still very thick and have their edges blunt. After the 1 

 18 dorsal vertebrae come 27, and perhaps more, whose spinous apo- 

 physea diminish progressively. In the lumbar vertebras the transverse 

 apophyses are very long ; afterwards they diminish by degrees on the 

 sides of the tail, and again become rather longer at its extremity, 

 apparently for the support of the tail-fin. It would seem that the 

 first three only belong to the loins. The fourth has towards its extre- 

 mity a facet, which ia probably destined for the attachment of the 

 pelvic bones, which last are well marked in the Dugong. They are 



Zoophagoua Cetaceans. The skull in the Dolphins is very much 

 elevated, very short and very convex behind. The occipital crest sur- 

 rounda the top of the head, and descends on each side on the middle 

 of the temporal crests, which are directed much more backward than 

 it is. This large and occipital surface is formed by the occipital, the 

 interparietal, and parietal bones, which early unite into one piece. 

 The parietal bones descend on each side into the temple between the 

 temporal and the frontal bones, and they there reach the posterior 

 aphenoid bone. In front and above, the parietals terminate behind 

 the occipital creat, and the maxillaries approaching on their side, what 

 appears of the occipital bone externally only represents a very narrow 

 band, which traverses the skull from right to left, and seems to dilate 

 at each extremity to form the wall of each orbit ; but on raising the 

 maxillary and nearly the whole of the anterior surface of the cranium, 

 the frontal bone will show itself much larger than it appears to be 

 externally. The nasal bones are two rounded tubercles let into two 

 | foasa: of the middle of the frontal, and iu front of which the nostrils 

 i are sunk vertically. The posterior and vertical surface of these nos- 

 ! trils is formed by the cribriform plate of the ethmoid bone, but it has 



