PEOFESSOE PLOWEE ON THE EECENT ZIPHIOID WHALES. 221 



In general arrangement these foramina correspond very closely with those of Hypero- 

 odon. In the Sperm- Whale the greater massiveness of the cranial walls, compared 

 with the brain-cavity, and the consequent greater distance that has to be traversed by 

 the nerve-canals, causes some alteration in the condition of the foramina, several (as in 

 the case of that for the seventh and eighth nerves) more completely coalescing into a 

 single aperture, at least at their cerebral ends, than in the smaller-headed Ziphioids. 



Dimensions of the Skull. 



inches. 



Extreme length of cranium 54 



Length of rostrum (from the apex of the preemaxillae to the middle of 



a line drawn between the anteorbital notches) 36 - 2 



Anterior end of vomer to anterior end of prasmaxillae 13*6 



From middle of hinder edge of palate (formed by pterygoid bones) to 



end of praemaxillge 43-2 



Greatest height of skull, from top of nasals to lower border of pterygoids 21 



Greatest breadth, across postorbital processes of frontals 27 



Breadth across zygomatic processes of squamosals 26 - 4 



Breadth between outer borders of suprafrontal processes of maxillse . . 24 - 6 



Breadth of occipital condyles 7 "5 



Breadth of foramen magnum 2*4 



Height of foramen magnum 2-5 



Breadth of exoccipitals 205 



Breadth of base of rostrum (between bottom of anteorbital notches) . .15-7 



Breadth of rostrum at middle 6 



Nasal bones, antero-posterior length 5 - 2 



Nasal bones, greatest breadth of the two 4 



Anterior nares, greatest width of the two 2 - 9 



Breadth between outer borders of prsemaxillae opposite nares . . . . 6-6 

 Breadth between outer borders of prsemaxillae at their widest part, in 



front of the nares 8-2 



Breadth between outer borders of prsemaxillse at middle of rostrum . . 3-6 



Mandible. — Length of ramus 49 



Length of symphysis 12*2 



Vertical height of ramus at coronoid process 8-3 



Apex of mandible projecting beyond apex of rostrum . . 2 - 7 



The rami of the mandible are not ankylosed at the symphysis. They are more 

 massive in form and of a denser substance than in Hyperoodon, especially near the 

 symphysis, corresponding with the greater development of the teeth. A slight irre- 

 gular groove, with numerous minute vascular canals opening into it, extends along the 



2k2 



