HISTORY OF WHALES 



199 



Egypt. Not merely the cast of the brain 

 but also those of the cavities and sinuses 

 in the region of the narial passages are 

 exposed to view. It is obvious that the 

 sense of smell was still of considerable 

 importance to this zeuglodont, as is 

 shown by the development and peculiar 

 elongation of the olfactory peduncles, 

 which are attached to the ventral surfaces 

 of the cerebral hemispheres in the charac- 

 teristic mammalian fashion. The rather 

 smooth cerebral hemisphere, which is 

 primarily an olfactory receptive mechan- 

 ism, is quite different from the convoluted 

 cerebrum of living odontocetes and mysti- 

 cetes. Only one investigator has had the 

 opportunity to study a series of endo- 

 cranial casts of Middle and Upper Eocene 

 zeuglodonts. On the basis of these casts, 

 Dart (192.3) has concluded that the 

 brains of late Eocene zeuglodonts show 

 that the loss of the sense of smell was 

 gradual and that this loss was accom- 

 panied by an excessive development of 

 the trigeminal apparatus, which in a 

 pelagic mammal provides much more in- 

 formation concerning food and enemies. 



The whalebone whales (Mysticeti) have 

 olfactory structures, but the retention of 

 the sense of smell may be due in a larger 

 measure to the actual mechanical construc- 

 tion of the skull (see page 44, fig. z) than to 

 the need of such organs, for the olfactory 

 structures seem to be adapted, as in terres- 

 trial mammals, for smelling through the 

 medium of air. Water never comes in 

 contact with the sinuses in which the 

 olfactory nerves are distributed, and no 

 odors other than those conveyed by 

 water could be recognized when the 

 whales are feeding below the surface. 

 We are therefore at a loss to conceive how 

 cetaceans may smell through the medium 

 of water, inasmuch as the olfactory 

 nerves are distributed in a rather simple 

 manner to the mucous membranes of the 



olfactory pouches, which hang downward 

 from the dorsal walls of the narial pas- 

 sages. Each of these olfactory diverticula 

 has a slit-like orifice. 



The archaic toothed whales of the 

 Upper Eocene have passages for olfactory 



S.oc. 



Fig. 2.1. Diagram Illustrating Position ov Endo- 

 cranial Structures in Skull or Prozeuglodon 



STROMERI 



Abbreviations: C, condyle; Ce., cerebrum; Cb., 

 cerebellum; C.La., lachrymal canal; f.opt., optic 

 nerve; F. spb., sphenoidal fissure; Fr., frontal; Ju., 

 jugal; Na., nasal; N.A., external opening of narial 

 passages; N>., nasoturbinal; Max., maxillary; Olf,, 

 olfactory lobe at end of stalk-like peduncle; Pa., 

 parietal; Pmx., premaxillary; S.fr., frontal sinus; 

 S.max., maxillary sinus; S.oc, supraoccipital; S.or.pr., 

 supraorbital process of frontal; Sq., squamosal. 



nerves on the fore wall of the braincase. 

 There may be some question as to the 

 actual size of the olfactory orifices on the 

 skull of Xenoropbus sloanii, for the ethmoid 





