BRIEF SKETCH OF THE TOOTHED WHALES. 91 



in the Sperm-Whale, and in Mesoplodon the halves of the 

 mandible may not be fused at all. 



The cervical vertebrse are free in the Susu, White Whale, and 

 in Monodon also, or with irregular unions, the atlas and axis 

 being free ; in Physeter the atlas alone is free, in Ziphius the 

 three anterior vertebrse are united, the rest are free ; in the 

 Porpoise the first to the sixth have coalesced, and sometimes the 

 seventh joins them. In Orca the bodies of the first and second 

 and sometimes the third are united ; while in Glohiocephalus 

 the anterior five or six are united. In Pseudorca the first to 

 sixth or seventh are united, and the bodies of the lumbar, 

 vertebrae are more elongated than in Orca. 



One of the most interesting features in connection with the 

 whales is their method of respiration, and it has been more or 

 less carefully investigated in the group now under consideration. 

 Air-breathing animals entirely confined to the water, where 

 they find their food and, moreover, have in its depths freedom 

 from pursuit, must of necessity present special modifications 

 of the typical mammalian organs. Externally, the Toothed 

 Whales have a single blow-hole or nostril, which is generally 

 transverse and crescentic, with the horns of the crescent point- 

 ing forward, though in the Susu it is longitudinal, linear, and 

 median, and in the Sperm-Whale longitudinal, /-shaped, and to 

 the left of the median line. The blow-hole closes by its own 

 elasticity, but opens by muscles. Except in the Sperm-Whale 

 the aperture is on the top of the head, far removed from the 

 usual position in mammals. The air is conveyed by the nasal 

 passages, which have sinuses or spaces, to the largyngeal appa- 

 ratus, the distal portion of which (arytenoid cartilages and 

 epiglottis) is remarkably elongated — forming, indeed, a tube 

 with an enlarged end — which is grasped by the muscles of the 

 soft palate, very much as in the young marsupial in the pouch. 

 Thus, when the blow-hole is closed and the larynx grasped, the 

 whales can swallow their food without the danger of admitting 

 water into the windpipe. They rise to the surface for air, pro- 

 jecting the blow-hole and blowing — that is, expiring the air from 

 the lungs and rapidly drawing in fresh air. The condensation 

 of the warm moist air from the lungs forms a column of vapour, 

 which shoots to a greater or less height in the air. In the case 



