248 CETACEA 
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 vertebra, 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 vertebra. (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 Physeterine.—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.—Upper teeth apparently of uncertain number, rudi- 
mentary, and functionless, being embedded in the gum. Lower jaw 
Fia. $2.—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 edoes 
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 
? Linn. Syst, Nat, 12th ed. vol. i. p. 107 (1766). 
