Prof. Eschricht on the Gangetic Dolphin. 177 



articulating surface for the under jaw. Immediately behind this 

 cavity is the deep canal for the cartilaginous meatus auditorius ; 

 behind this again are two bony, obtuse processes, of which the 

 foremost (PI. VII. fig. 1 t) is the mastoid process of the tem- 

 poral bone, and that behind, the so-called processus jugularis of 

 the occipital bone, more correctly the hyoid process, because on 

 it the cartilaginous os hyoideum is firmly grown. Between these 

 two processes and the pars petrosa is the great foramen lacerum 

 posticum for the transmission of the vena jugularis interna, to- 

 gether with the ninth, tenth and eleventh pairs of cerebral nerves, 

 and, quite internally, in the semitubular hook between the hyoid 

 process and the wing-formed lateral part of the basilar portion 

 of the occipital bone (PI. VI. fig. 3. before the bulla tympani g) 

 for the twelfth pair. The condyloid processes of the occipital 

 bone are equally bent upwards and downwards, so that they are 

 equally conspicuous whether the cranium is viewed from above 

 or from below. They are seen in their entire extension from 

 behind (PL VI. fig. 3 k) on each side of the large, almost square 

 foramen occipitale {ibid, x), whose inferior margin, however, is 

 deeply excavated in the middle. A large aperture (foramen con- 

 dyloideum posticum) is seen on the smaller cranium, above each 

 articulating surface ; on the larger cranium only above that on 

 the right side. By throwing a strong light into the foramen 

 occipitale, all the elevations and depressions, as well as the 

 entire bony structure, may be seen on the inner surface, even 

 in the unopened cranium. In most respects I can discover no 

 essential peculiarities from other dolphins. The tentorium cere- 

 belli is ossified only to a small extent ; the falx cerebri more ex- 

 tensively. The posterior sphenoid bone seems to be one with 

 the basilar part of the occipital bone, as is the ethmoid partially 

 with the frontal and anterior sphenoid bones. The whole ante- 

 rior cerebral cavity is formed of the frontal bones and partly the 

 ethmoid bone ; and the side walls of the parietal bones, between 

 which is seen, above, a small interparietal bone. The temporal 

 bones cannot be clearly made out. Besides the said large foramen 

 occipitale and the two foramina lacera, together with the aper- 

 tures on the pars petrosa temporum for the seventh and eighth 

 pairs of nerves (not to mention in this place the so-called aquseduc- 

 tus), there are only three large apertures on each side. The fore- 

 most is situated between the anterior and posterior sphenoid bones; 

 the middle one (proceeding backwards in the series) pierces their 

 large wings; both are placed rather outwardly and are directed from 

 behind forwards, through the pterygoid bone, and serve mani- 

 festly for the transmission of the chief branches of the fifth pair 

 of nerves, answering to the foramina rotundum and ovale. The 

 hindermost aperture is placed considerably outwardly between 

 Ann. §• Mag. N. Hist. Ser. 2. Vol. ix. 12 



