30 PROCEEDINGS OF THE NATIONAL MUSEUM vol. G& 



briiim. On the dorsal surface of the tubercle (fig. 10) near the 

 anteroexternal angle and at the end of the groove which traverses , 

 the malleus in front of the articular facets is a small circular de- 

 pressed area for the insertion of the tensor tympani tendon. Below 

 and near the antero internal angle, the manubrium (fig. 11) is repre- 

 sented by a blunt recurved process, pointing downward and back- 

 ward, and flattened against the side of the malleus. To a small 

 triangular area near the apex of the manubrium was attached the 

 fleshy process (the "triangular ligament" of authors) of the mem- 

 brana tympani. Some of the fibres of the fleshy process may be 

 attached in the short narrow groove below the manubrium. The 

 manubrium is slightly more developed than in Prodelphinus malmj- 

 anus. In living whales, according to Ridewood, the extremity of 

 the manubrium is attached by fibrous tissue to the middle of the 

 dorsal surface of the tympanic membrane. The head of the malleus 

 is borne on a slender stalk (fig. 8), the processus anterior (longus^ 

 gracilis, and folianus of authors), which becomes narrower as it 

 approaches the outer lip of the tympanic bulla, fusing with the latter 

 in the narrow groove between the sigmoid process and the uncinate 

 l)rocess. The malleus, including the anterior tubercle, measures 5.8 

 mm. in leno:th and 4.2 mm. in width. 



From the position of the articular surface on the head of the mal- 

 leus, the incus (fig. 11) lies above and internal to it, with the smallest 

 articular facet on the ventral face of the body. Its articular surface 

 has facets divided by a sharp ridge. Two distinct facets comprise 

 the surfaces by which the incus is fitted to the malleus. The largest 

 (fig. 15) of these two facets is shallowly concave, subcrescentic in out- 

 line, and is coextensive with the external face or base of the body 

 of the incus; the smallest facet (fig. li) is deeply concave and is 

 situated at the base on the ventral side. Curiously enough these two 

 facets are quite similar in appearance and shape to those on the 

 incus of Prodelphinus malanjamus. The body of the incus is feebly 

 developed, being absorbed by the crus longum. The crus breve 

 (figs. 11, 15, 16, 17) is thin, slightly curved, expanded distally, with 

 an elongate facet on the dorsal surface of the apical portion (fig. 10) 

 which rests in the fossa incudis. The crus longum (figs. 14, 17) is 

 not as thick as in Prodelphinus, the ventral surface is less convex, 

 and the facet (fig. 10) for articulation with the head of the stapes 

 is small and is situated on the dorsal face near the apex. From the 

 apex of the crus longum to the base of the body the incus measures 

 3.2 mm. and the greatest diameter of the base is 2.8 mm. 



