ATJDITORT OSSICLES Or EHTTINA STEI/LEEI. 



369 



the malleus of Bliytina. The ' Vega ' specimen, being the more 

 perfect, has been selected for this purpose. 



Antero-posterior measurement of 



malleus (root of mamibrium to 



root of processus gracilis). . . . 

 Measurement from manubrium 



to most internal part of body 



of malleus , 



Length of manubrium 



) 



The incus, both in the ' Vega ' and the American specimen, is 

 very similar to the same bone in Manatus. The body is shallow 

 and wide between the crura. There is not the prominence behind 

 the upper and more posterior o£ the two lower facets so conspi- 

 cuous in Halicore ; so that the posterior part of the body is not 

 larger than in the otherwise much smaller incus of Halicore. The 

 upper facet is wider and deeper than in Manatus, but, as far as I 

 could judge (not being able to disarticulate the bone from the 

 malleus), of much the same shape. Its dimensions were as fol- 

 lows : — 



Distance betwen Depth of body to 

 extremities of point of 



crura. proc. brev. 



Rhytina 2-4 



Manatus 1*6 



Halicore 1*6 



1-5 

 1-2 

 1-0 



(As it is difficult to fix a precise "root" to the processus brevis, the 

 "depth" is taken from the highest part of the body to the extremity 

 — that is, to the point of ankylosis — of that process.) 



Lastly, in the American specimen the stapes existed. It fell 

 out of its place in examination, which proved convenient, as will 

 be seen; moreover it was readily replaced. In shape it is very 

 similar to the stapes of Manatus senegalensis. The head is 

 equally well developed, and bears an almost circular articular 

 surface 0'5 centim. in diameter (0"4 centim. in Manatus^ As in 

 Manatus, also, both crura are long and hardly divergent ; both 

 also are crooked ; the anterior, too, is the straighter, and is much 

 thinner in proportion to the posterior than even in Manatus. 

 The posterior crus is very bulky, and bulges higher up than in 

 Manatus ; the thickness of this crus encroaches upon the aperture, 

 which is therefore much smaller proportionately than in the 



* The greater curving of the manubrium in this Sirenian, compared with 

 Bhytina, must be taken into account, as the extremities are thereby approxi- 

 mated. 



