638 



3918. The os penis of a Walrus. Hunterian. 



3919. The pubic extremity of the os penis of a Walrus, longitudinally bisected. 



Purchased. 



Genus Cystophora. 

 Dental formula : i ?=?, c ^, m g=30. 



3920. The skull of the great Proboscis -Seal, or Sea-Elephant (Cystophora pro- 

 boscided). 



Besides its superior size, it differs from that of the Cystophora cristata, No. 3935, in the 

 form and proportions of the palatine bones, the posterior borders of which present three 

 notches ; in the relatively shorter extent of the nasal processes of the premaxillaries ; in the 

 greater prominence of the antorbital processes of the maxillaries ; and the absence of the 

 depression beneath the antorbital foramen. The enamelled summits of the teeth are smoother, 

 those of the middle molars presenting only two grooves on the outer side, which converge to 

 the point. The superior dimensions of the teeth are chiefly due to the expansion of their 

 fangs, which are simple and covered with a very thick mass of cement. The sagittal crista 

 is scarcely indicated, the temporal ridges terminating at the sides of the sagittal suture, but 

 the occipital crest is conspicuous for its great height and thickness ; the lower border of the 

 superoccipital presents two vertical venous perforations, which are likewise present in the 

 skull of the young Cystophora. Traces of the suture between the basisphenoid and the basi- 

 occipital and between the basisphenoid and presphenoid still remain. The entocarotid canals 

 at the back part of the petrosals are very conspicuous : there are no ectocarotid canals. The 

 paroccipitals are less prominent than in the Cystophora cristata. The occipital condyles meet 

 upon the basioccipital. 



Purchased. 



3921. The skull of the great Proboscis-Seal (Cystophora proboscidea). 



The posterior border of the bony palate presents two notches ; the smaller middle notch is 

 hardly perceptible in this skull. 



Mm. Brookes. 



3922. The cranium, transversely bisected across the tympanic cavities, of the great 

 Proboscis-Seal ( Cystophora proboscidea) . 



The posterior section shows the rudimental development of the bony tentorium, as com- 

 pared with that in the Otaria leonina, No. 3971, the great thickness and coarse diploe of the 

 walls of the cranium formed by the parietals, the extremely small proportion of the squa- 

 mosal which enters into the formation of those walls, and the dense structure of the mastoid, 

 where it coalesces with the base of the zygomatic process. The two orifices of the vertical 



