178 Prof. Eschricht on the Gangetic Dolphin. 



the large wings of the sphenoid bone and the occipital bone ; and 

 it is at once evident, from this position of the foramina, and their 

 very strongly developed processus clinoidei, that they serve for 

 conveying the carotis cerebralis. 



There is, besides, a large number of apertures on the inside of 

 the skull, especially anteriorly in the frontal part, manifestly for 

 the transmission of blood-vessels. The ethmoid bone rises in 

 the median line in the form of alow, but broad crest (crista galli), 

 having on each side some small holes, one on the left side, two 

 on the right, large enough to admit a knitting-needle. Our 

 dolphin, therefore, has most probably olfactory nerves like the 

 Hyperoodon, contrary to what obtains in other species. There 

 are two symmetrical, but not particularly large holes between 

 the ethmoid and the wings of the anterior sphenoid bone, 

 answering to the far greater holes in the same parts in whales 

 generally. But the most essential and remarkable feature in the 

 cavity of the skull of the Gangetic dolphin is this, that the holes 

 for the optic nerves are only rudimentary. Indeed they are scarcely 

 to be discovered except by a careful search assisted by their known 

 locality and form. In size they are not at all larger than most 

 of the other holes (for the transmission of blood-vessels) in the 

 sphenoid and surrounding bones ; they are much smaller than 

 those in the frontal bone, and are to be recognized by their 

 symmetrical position on each side of the base of the wings of the 

 small sphenoid bones, but especially by their form of transversal 

 fissures having the upper margin projecting. Only in the smaller 

 of the crania which I had at my disposal, did I succeed in in- 

 troducing a stiff hair through them into the orbits ; and this 

 most striking minuteness of the holes for the optic nerves, at once 

 points out that the latter must be rudimentary in the Gangetic 

 dolphin — a most remarkable circumstance. 



The great similarity of the under-jaw with that of the Cachalot 

 is very striking, both as regards its extreme narrowness and the 

 consequent proximity of the two rows of teeth, and also the 

 length of the symphysis, being little more than two-thirds of 

 the whole under-jaw. Behind this long junction the side- 

 branches diverge in a slightly curved direction (PI. VII. fig. 1 w), 

 the posterior half assuming the figure of a shovel, its upper 

 margin rising for the insertion of the temporal muscle, and re- 

 presenting a much-elongated processus coronoideus, while its 

 lower margin, which is slightly bent outwards, appears like a flat 

 osseous wing on its outer third part (PI. VII. fig. 1). The 

 condyloid process is on the posterior margin, and like the 

 side-branches, it is quite hollow, the entrance to their cavity, as 

 is generally the case among dolphins, occupying nearly the whole 

 posterior third of the inner plate of the branches. 



