220 PROFESSOR FLOWER ON THE RECENT ZIPHIOID WHALES. 
cerebri, which, in the figure, conceals the real height of the lateral parts of the cavity. 
A well-marked ridge, more conspicuous than in /yperoodon, commencing on the orbito- 
sphenoid below, and extending upwards on the frontal almost to the vertex, divides the 
anterior from the posterior cerebral fossa. The cerebellar fossa is relatively larger than 
in J/yperoodon, and is separated from the posterior cerebral fossa by a strong ridge. 
There is no olfactory fossa. 
The periotic bone is excluded from the cerebral cavity by a distance of 34 inches. 
The foramina which pierce the base of the cranium, as seen from within, are :— 
1. A very small hole, } inch from the middle line, and 5 inches in front of the suture 
between the presphenoid and basisphenoid, and passing through the posterior lateral ex- 
pansion of the mesethmoid which corresponds to the cribriform plate of other mammals, 
to the nasal passage, may be an olfactory foramen. A similar foramen has been noticed 
in Ziphius by Fischer, and exists on a larger scale in Physeter’. 
2. The optic foramen is a rather small oval fissure (0°4 inch by 0°3 inch) perforating 
the orbito-sphenoid, near its hinder border, and soon joining the great orbital or 
sphenoidal fissure. It is less than half the size of the corresponding opening in 
Hyperoodon. 
3. Immediately behind the sharp ridge formed by the hinder edge of the orbito- 
sphenoid is the large funnel-shaped opening, compressed from side to side (about 1 inch 
by 4 inch in diameter at the narrowest part), corresponding to the sphenoidal or 
orbital fissure together with the foramen rotundum, as it transmits the nerves to the 
orbit, as well as the middle division of the fifth nerve. 
4, The foramen ovale, for the third division of the fifth, forms a distinct perforation 
through the alisphenoid, about 0°3 inch in diameter. It is connected with the last by 
a shallow groove. 
5. Behind the orbito-sphenoid is a large infundibuliform depression, divided at the 
bottom into an anterior smaller circular aperture (0°35 inch in diameter) and a posterior 
larger oval opening (1 inch by 0-4 inch). ‘The former is for the seventh nerve, 
which it conducts to the meatus auditorius internus on the periotic; the latter for the 
various nerves commonly known as the eighth pam; this is further divided near its 
termination on the surface by a narrow bony septum. 
6. Immediately behind the last, in the cerebellar fossa, and 1? inch from the middle 
line, is the small condylar foramen (0-3 inch by 0:2 inch in width) for the hypoglossal 
nerve. After a course of about four inches through the bone, it opens into a groove in 
the hinder surface of the skull between the basioccipital and the exoccipital. 
7. In the basisphenoid, 1 inch from the middle line, opposite the prominence in 
front of the sella turcica (twberculum selle) is the longitudinal narrow oval aperture 
(0°4 inch by 0-2 inch) for the carotid artery. This canal opens externally in the 
pterygoid close to its posterior border. 
' See “ Osteology of the Sperm Whale (Physeter macrocephalus),” Trans. Zool. Soc. yol. vi. p. 316. 
