248 GET ACE A 



to form an elevated prominence or crest behind the nares. Pterygoid 

 bones thick, produced backwards, meeting in the middle line, and 

 not involuted to form the outer wall of the post-palatine air-sinuses, 

 but simply hollowed on their outer side. Anterior facet of periotic 

 bone (Fig. 87) for articulation with the tympanic quite smooth ; 

 and the posterior tympanic surface of the former broad, with a 

 median longitudinal ridge. Transverse processes of the arches of 

 the dorsal vertebrae, to which the tubercles of the ribs are attached, 

 ceasing abruptly near the end of the series, and replaced by 

 processes on the body at a much lower level, and not on a line or 

 serially homologous with them, but serially homologous anteriorly 

 with the heads of the ribs, and posteriorly with the transverse 

 processes of the lumbar vertebrae. (In some genera, as Physeter, 

 the two processes, upper and lower on each side, are both present 

 and well developed in the same vertebra in the region of transition. 

 In others, as Ziphius and Berardius, they are not both developed on 

 any single vertebra.) Costal cartilages not ossified. 



Subfamily Physeterinse. Numerous teeth in the mandible, 

 which are not set in distinct bony alveoli, but in a long groove 

 imperfectly divided by partial septa, and held in place by the 

 strong, fibrous gum surrounding them. No distinct lachrymal bone. 

 Cranium strikingly asymmetrical in the region of the narial 

 apertures, in consequence of the left opening greatly exceeding the 

 right in size. 



Physeter. 1 Upper teeth apparently of uncertain number, rudi- 

 mentary, and functionless, being embedded in the gum. Lower jaw 



FIG. 82. Skull of Sperm Whale (Physeter macrocephalus). 



with from 20 to 25 teeth on each side, stout, conical, recurved, and 

 pointed at the apex until they are worn, without enamel. Upper 

 surface of the cranium concave ; its posterior and lateral edges 

 raised into a very high and greatly compressed semicircular crest 

 or wall. Zygomatic processes of jugal bones thick and massive. 

 Rostrum greatly elongated, broad at the base, and gradually tapering 



1 Linn. Syst. Nat. 12th ed. vol. i. p. 107 (1766). 



