572 



CETACEA. 



ble or triple ridges, and with the 

 root distinct from the crown, pre- 

 senting a remarkable resemblance 

 to those of some of the Pachy- 

 derms, as the Hippopotamus. The 

 Dugongs have simple elliptical 

 molares, the crown of which, before 

 it is worn, presents two slight fur- 

 rows, which are entirely effaced 

 by age. They are without fangs, 

 properly so called ; and in the up- 

 per jaw are found two long tusks, 

 of which the other Cetaceans of 

 this family are destitute. The 

 Rytince have no molares at all; these teeth 

 are replaced by a horny plate in the middle 

 of each jaw, a structure which seems to connect 

 these animals with the Whalebone Whales. 



The tongue is short and but little susceptible 

 of movement. 



The os hyoides is characterized in the Cetacea 

 chiefly by the slight degree or total absence 

 of connection with the larynx, resulting from 

 the elevated position of this organ required by 

 its peculiar relations with the posterior nares. 



In the Herbivorous order the Dugong pre- 

 sents a simple form of the os hyoides ; the 

 posterior cornua soon anchylose with the body, 

 but send no ligament to the thyroid cartilage. 

 The anterior cornua generally remain cartila- 

 ginous, and form the medium of union be- 

 tween the body or basi-hyal, and the large and 

 long styloid processes. In the Delphinidis the 

 body and posterior cornua of the hyoid bone 

 are of a flattened form. In the Balenidie, as 

 the Piked Whale or Baloenoptera, the body 

 (a, Jig. 258) is a cylindrical bone, extended 



Fig. 258. 



Fig. 259. 



Tongue and Baleen-plates of the Piked Whale, 

 Balcenoptera Boops.* 



The genio-glossi pass backwards and inwards 

 from the anterior contour of the lower jaw. 



The tongue itself corresponds to the form 

 of the space included by the rami of the lower 

 jaw, and is consequently of great size in the 

 Cachalots and Balaenidae, rising in the latter 

 like an immense cushion (a, Jig. 259), into 

 the space between the laminse of baleen (6), 

 and affording a great quantity of the finest oil. 

 In the figure it is represented in the Piked 

 Whale, but probably preternaturally enlarged 

 and raised by the extrication of gas caused by 

 putrefaction. It is thick, and its free extremity 

 is generally short, but this is less remarkable 

 in the Phytophaga than in the Zoophaga. In 

 the Dugong (jig. 260) the upper surface of 

 the anterior part of the tongue () is beset with 

 cuticular spines, and on each side of its basis 

 there is a remarkable horny retroverted pointed 

 process (b, 6). 



Pig. 260. 



Hyoid bones of the Piked Whale. 



transversely, and is slightly curved backwards 

 and upwards; its middle portion supports an- 

 teriorly two processes (b, b) resembling the 

 base of the anterior cornua in the Ruminants ; 

 besides these there are, in this genus, two 

 rounded tubercles on the posterior margin op- 

 posite these processes. The styloid bones 

 (c, c) are cylindrical and slightly curved in 

 two directions ; they are joined by cartilage 

 on each side to the occipital protuberance 

 which represents the mastoid process. 



The muscles which protrude and retract the 

 tongue are extremely simplified in the Ce- 

 taceans ; the retractors are represented by a 

 single pair, analogous to the stylo-hyoidei, the 

 fibres of which pass from the posterior margin 

 of the stylo-hyal bones to the body of the 

 hyoid. The stylo-glossi pass from the anterior 

 and superior margin of the styloid process to 

 their insertion. The hyoglossi arise from the 

 middle of the convexity of the os hyoides. 



Tongue of the Dugong. 



In the Porpesse the surface of the tongue is 

 soft and smooth, and very flat superiorly; the 

 anterior margin is fringed by a number of short 

 irregular processes (a, fig. 265). 



The salivary glands are reduced to the most 

 rudimental condition. 



In the Phytophagous Cetaceans the stomach 

 is separated into two portions (fig. 261); one, 

 the cardiac (a), very large, the other, the 

 pyloric (6), of narrower calibre, by a contrac- 

 tion (c) giving origin to two prolongations 

 (d, d), which are tubiform in the Dugongs, 

 and of a pouch-like form in the Manatees. 



In both species there is a gland at the 

 cardiac extremity of the stomach (c), which in 

 the Dugong, Sir Everard Home (from whose 

 memoir the figure subjoined is taken) describes 

 as " forming a round mass, as in the Beaver. 

 The orifices of these glands are small, and 



* From Fr. Cuvier, Cetacea, pi. 20. 



