. Bulletin - United States National Museum. Science. CETOTHERES FROM THE MIOCENE CHOPTAISTK FORMATION above and in front of the anterointernal rim of the entrance to the mandibular canal. The condyle (106X164 mm.; fig. 2) of the type left mandible is large, expanded transversely in an oblique direction above the middle of its vertical diameter and is more convex from side to side than dorsoventrally. Above the protuberant and convex angle, the deep groove for the attachment of the internal pterygoid muscle tends to impart a contour to the internal edge similar to the external edge of the condy
. Bulletin - United States National Museum. Science. CETOTHERES FROM THE MIOCENE CHOPTAISTK FORMATION above and in front of the anterointernal rim of the entrance to the mandibular canal. The condyle (106X164 mm.; fig. 2) of the type left mandible is large, expanded transversely in an oblique direction above the middle of its vertical diameter and is more convex from side to side than dorsoventrally. Above the protuberant and convex angle, the deep groove for the attachment of the internal pterygoid muscle tends to impart a contour to the internal edge similar to the external edge of the condylar articular surface. Dorsally the attenuated condylar articular sur- face merges anteriorly with the curved thin rim of the horizontal ramus behind the coi-onoid process, and al- though narrowed is actually more noticeably trans- versely thickened than on Calvert mandibles of similar length. The forward curving internal and external bor- ders of the condyle project noticeably beyond the lateral surface of the adjacent portions of the ramus. One may assume that this condyle was enveloped by a thick fi- brous pad, similar to that of Recent mysticetes (Turner, 1892, p. 69), which served as the means of attachment to the glenoid fossa of the zygomatic process. Table 4.—Measurements {in mm.) of left mandibles Figure 2.—Posterior view of con- dyle of left mandible, USNM 23794, of Thinocetuj arthritus. an, angle; cm., condyle of man- dible; , groove for internal pterygoid Of the several mysticete mandibles recovered during the excavations in the Antwerp basin, this Choptank mandible exhibits the closest resemblance to Mesocetus pinguk (Van Beneden, 1886, pi. 44, fig. 10; right con- dyle, mm.), except that the angular portion of the condylar articular surface below the inner groove for attachment of the internal pterygoid muscle is nar- rower and prolonged farther downward. The vertical diameter (123 mm.) of the anterior end of the right mandible of M
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