44 



Cranium. 



Length of the cranium 



From the occipital crest to the upper border of 



the nasal aperture 



Length of nasal aperture 



Breadth of ditto 



From the lower border of the nasal aperture to 



the end of the intemiaxillary bone 



Breadth of occijmt 



Smallest mterspace of the temporal ridges 



Greatest distance bet«'een zygomatic arches 



Greatest distance betvveen postorbital processes 



of the frontai bone 



Lotoer Jaw. 

 From the condyle to the lower part of the »t/m- 



phr/sis 



From the condyle to the base of the ascending 



ramus 



Breadth of ascending ramt<« 



Length of dental (molar) series 



Length of sloinng SĮ/mph t/gis 



Breadth of ditto 



From outside of one condyle to that of the other 

 From the condyloid to the coronoid process 



in. lin. 

 14 6 



O 

 O 

 O 



811 

 10 



211 

 4 



11 3 



6 G 

 3 O 

 2** O 

 5 2 

 2 3 



7 O 

 2 7 



" The short and thick neck, fin-like fore-legs, \vant of hind-legs, 

 caudal tegumentary fin, smooth, naked, and almost hairless integu- 

 ment, are all modifications of external form, by Avhich the Dugongs 

 and Manatees are adapted to play their part in the waters : but the 

 kind of part which they are to play in that element depends on or- 

 ganic characters which mainly if not exclusively reveal their true 

 affinities. Now w'e have seen that the whole of the intemal struc- 

 ture in the herbivorous Cetacea differs as widely from that of tlie 

 camivorous Cetacea, as do their habits : that the amount of varia- 

 tion is as great as well could be in animals of the šame class, exist- 



* Deciduous and permanant tiisks in place ; the first molar, left side, 

 lower jaw shed. Outer wall of sockets of permanant tusks entire. 



t Deciduous tusks shed and their sockets obliterated ; the points of the 

 permanent tusks protruding from their sockets : the s]iallow cavity at their 

 base exposed by the absorption of tha wall of the socket at that part. 



X Sockets of deciduous tusks oblitarated, permanent ones protruded to 

 the usual extent and worn by use : their sockets entire. 



§ This dimension increases as the intermaxillary bones are lengthened 

 in the antero-posterior direction. 



II The increase of this dimension is due to the greater development of 

 the lower part of the intermaxillary bones in correspondence \viih the sexual 

 condition of the tusk. 



^ This dimension of course diminishes with the increased development 

 of the temporal museles conseąuent upon the fitness of tha tusk for use. 



«* The increasing breadth of the lašt molar compensates for the loss of 

 the small anterior molars. 



