SKELETON OF SIRENIA. 



433 



of existing Sirenia.^ Steller assigns to it six cervicals, as in 

 Manatus. Nine pairs of ribs are said to have joined the sternnm. 

 B. Skull. — The facial or rostral part of the skull, anterior to 

 the orbits, is short, especially so in Manatus, fig. 239, in which it 

 slightly descends : in Halichore, figs. 292, 294, 22, it is bent down 

 more abruptly: in Rhytina the angle of the upper contour of the 

 rostrum is greater than in Manatus, that of the lower contour less 

 than in HalicJwre, exemplifying, as in other parts of the skeleton, 

 an intermediate character. All the skull-bones are massive in 

 Siren ia, and, save in the in- 



293 



stances of anchylosis, are 

 somewhat loosely connected 

 too;ether. In the Dugono; the 

 basioccipital, fig. 294, 1, is a 

 triradiate bone, the two short 

 rays diverging posteriorly to 

 join the exoccipitals, and 

 formino' the lower end of each 

 condyle. The exoccipitals, 2, 

 almost meet above the fora- 

 men magnum ; they have a 

 short rough paroccipital pro- 

 cess. The superoccipital, 3, 

 is early anchylosed to the 

 parietals, which have equally 

 coalesced into a sino^le sub- 

 quadrate -massive bone, fig. 



293, 7, with the sides bent 

 down at nearly a right angle 

 with the almost flat upper 

 part, which is perforated by a ' foramen parietale.' A falciform 

 ridge descends from the inner surface. The basisphenoid, fig. 



294, 5, has coalesced with the alisphenoids, wliich are grooved 

 both behind and before, not perforated, by the trigeminal nerve. 

 The massive pterygoids are anchylosed to the base of the ali- 

 sphenoids : the posterior ends of the palatines, which are wedged 

 into the interspace between the ento- and ecto- pterygoid pro- 

 cesses, send upward a part wliich appears in the temporal 

 fossa behind the maxillary. The presphenoid, as a compressed 

 ' rostrum,' is wedged between the lamln;i3 of the vomer, and has 

 coalesced with the confluent orbitosphenoids which it supports. 

 There is no ' sella turcica.' The orbitosphenoids are perforated 



Skull of Dugoi 



{Ualicliorc indicus). 



VOL. II. 



xciv. p. 

 F P 



95. 



