. Bulletin - United States National Museum. Science. PARIETOBALAENA PALMERI 185 for identification. Lengths of the bullae of this species range from 52 to 63 mm. Other minor differences may be attrib- uted to age factors. Measurements (in mm.) of the tympanic bullae are as follows: USNM USNM USNM USNM USNM 10668 16119 10677 13874 15576 Greatest length of bulla Greatest width of bulla Greatest vertical diameter on external side, ventral face to tip of sigmoid process Greatest length of tym- panic cavity Left Right Right Right Left 57 59 — 36 35 33 .— 43 45 49 44 42 44 4
. Bulletin - United States National Museum. Science. PARIETOBALAENA PALMERI 185 for identification. Lengths of the bullae of this species range from 52 to 63 mm. Other minor differences may be attrib- uted to age factors. Measurements (in mm.) of the tympanic bullae are as follows: USNM USNM USNM USNM USNM 10668 16119 10677 13874 15576 Greatest length of bulla Greatest width of bulla Greatest vertical diameter on external side, ventral face to tip of sigmoid process Greatest length of tym- panic cavity Left Right Right Right Left 57 59 — 36 35 33 .— 43 45 49 44 42 44 46 Periotic Likeness of cetothere periotics without some degree of relationship seems unlikely. The degree of affinity may be assessed by noting the extent of resemblance of auditory structures that appear to be less susceptible of modification during growth. For example the shape of the pars cochlearis of this species exhibits very little change in the growth stages from new born to adult. The most obvious alteration occurs in the shape and dimensions of the posterior process (fig. 84), which is firmly wedged in a deep groove between the exoccipital and the postglenoid portion of the squamosal. Nine periotics either attached to or associated with skulls or crania were selected to illustrate the range of individual variation. A similar type of pars cochlearis is found in the Belgian Anversian "Idiocetus" laxatus (Van Beneden, 1886, pi. 54, figs. 3, 4). On the posterior face of the pars cochlearis above (dorsal to) the foramen rotunda and its projecting shelf and behind the stapedial fossa is a short, narrow fossa (vertical diameter, 4 to 8 mm.) of variable depth that extends from the internzJ end of the posterior process to the inner (cerebral) face of the periotic (fig. 87b). It is separated from the fossa for the stapedial muscle by the thin crestlike posterior ridge bounding the latter. This fossa extends upward and inward fi-om the fossa for the stapedial
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Keywords: ., bookauthorun, bookcentury1800, bookdecade1870, booksubjectscience
