NO. 8 INTERRELATIONSHIPS OF THE CETACEA WINGE I3 



not widened so as to encroach on the parietal. The mastoid is still 

 visible on the outer wall of the braincase. Occipital crest well 

 developed, projecting. Occipital condyles not pressed flat. On the 

 basal part of the occipital the impressions where the lower neck 

 muscles were attached are essentially unmodified in character, and the 

 under side of the occipital bone's basal part is not shaped for sheath- 

 ing the gullet and larynx. On the other hand the exoccipital has 

 already acquired a noticeable widening out to the side. The hinder 

 part of the nasal cavity appears to be wholly undisturbed ; it must 

 contain a well-developed ethmoid. The bony palate is already pro- 

 longed backward by plate-like outgrowths fi:om the lower margin of 

 both the palatine and the pterygoid. No doubt an air-sac formed by 

 an enlargement of the nasal passage lay on the outer side of the 

 pterygoid, but whether it was enclosed by outgrowths from the 

 adjacent bones is doubtful. The tympanic bone had already acquired 

 the characteristic cetacean thickening of the inner wall. The cervical 

 vertebrae are mutually free, not strongly compressed. The odontoid 

 process of the axis is strong, projecting. The spinous processes of 

 the dorsal vertebrae differ noticeably among themselves as to their 

 slant, some of them sloping strongly backward, others upright or 

 directed a little forward ; those on the hindmost dorsal vertebrae are 

 rather low. Zygapophyses apparently well developed. No project- 

 ing transverse processes on the hindmost thoracic vertebrae. Centra 

 of ordinary size. On the tip of the transverse process of a sacral 

 vertebra there is present a rather large area of attachment for the 

 ilium, although the process has otherwise already lost much of its 

 original character. On such ribs as are present in the fossil there is 

 a well-developed capitulum ; the hindmost ribs lack the tuberculum 

 and are articulated with the corresponding vertebrae by the capitulum. 

 Proseuglodon (Zcuglodon osiris, Prozeiiglodon atrox partim'"), 

 also Eocene, Egyptian, has departed in dental characters not a little 

 from Protocetus. In the number of teeth the difference is only that 

 m^, small in Protocetus, is here absent. The form of the teeth has 

 undergone greater change : pm^ has lost the compressed form of the 

 crown and has become simply conical with a single root like the 

 incisors and canine ; pm- has acquired a serrate posterior margin ; 

 pm^, pni*, m^ and m^ are strongly serrated on both the anterior and 

 posterior margins of the crown ; in pm^ and pm* the inner heel is 

 much reduced and in the two molars it has entirely disappeared. The 

 lower jaw is also known ; it contains the typical 1 1 teeth. Incisors, 

 canine, and pm^ approximately uniform, simply conical ; pnio, pmg 



