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 Hyperoodon, 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 Hyperoodon, 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 3 J 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 3 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 1 . 



2. The optic foramen is a rather small oval fissure (04 inch by OS 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 ^ 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 (03 inch in diameter) and a posterior 

 larger oval opening (1 inch by 04 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 pair; 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 If inch from the middle 

 line, is the small condylar foramen (03 inch by - 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 (tuberculum sellce) is the longitudinal narrow oval aperture 

 (04 inch by - 2 inch) for the carotid artery. This canal opens externally in the 

 pterygoid close to its posterior border. 



1 See " Osteology of the Sperm Whale (Physeter macrocep^^alus), , ' Trans. Zool. Soc. vol. vi. p. 316. 



