174 Prof. Eschricht on the Gangetic Dolphin. 



goid bone extends up to the temporal * and the parietal bones f ; 

 and that below, it covers the large wing of the sphenoid bone %, 

 and forms even part of the basis of the cranium, namely the 

 furrow for the fifth pair of nerves §. In other whales (such as 

 the broad-headed, for instance, the Narwhale and Delphinus 

 globiceps), the large wings of the sphenoid are only in part 

 covered by the pterygoid ; so that above, in the temporal cavity, 

 they appear free between the frontal, temporal, and the parietal 

 bones, as in man ; although inwards, and in their greatest extent, 

 they are here entirely covered by them ; that is, in crania whose 

 inner, very thin and fragile plate of the pterygoid bone is un- 

 injured. 



Cuvier's assertion that " les sinus places sous les narines " are 

 only closed below by a membrane, is perfectly correct, except that 

 this membrane is throughout interwoven by a delicate bony net. 

 Both these must be considered, further, as part of the plate of 

 the pterygoid bone, and thus the remark of Cuvier, that the 

 pterygoid bones in the Gangetic dolphin seem to him not to be 

 recurved from below in order to cover the said " sinus " under the 

 nostrils below, falls to the ground. It is certain, moreover, that the 

 exterior bony or palatal wall of these " sinus " likewise belongs to 

 the pterygoid bone. The same holds good with all other Cetacea 

 and several mammalia not of that order. A bagshaped elonga- 

 tion proceeds sometimes from the cavity of the tympanum, or the 

 Eustachian tube, towards the pterygoid bone. Where this con- 

 sists of only one plate, as in the horse, it represents always the 

 inner wing, and the bag is applied to its outer surface. But in 

 Bradypus didactylus and Myrmecophaga Tamandua the bone con- 

 sists of two distinct plates, leaving a cavity between them, into 

 which the bag penetrates from behind. This is likewise the 

 case in all whales, only that an extraordinarily thick, dense vas- 

 cular net accompanies the bags, which, together with the tym- 

 panic cavities, are filled with blood and a number of strongyli ; 

 at least in the dead body. The proper entrance to these cavities, 

 being the only one which, with its soft parts, is not closed up by 

 any membrane, is always directed backwards, exactly against the 

 petrous portion of the temporal bone and the bulla tympani. 

 The sinus in question, under the posterior nostrils, belong, there- 

 fore, always and essentially to the pterygoid bones ; and where 

 they are situated outside these, as in the horse, the place of the 

 outer plate is supplied by a membrane. But this does not pre- 

 vent the excavation from penetrating deeper into the palatal 

 bones, which actually takes place in dolphins generally (not 



* Fifth Memoir on the Whales, p. 255, 256, t. 12. f. 3 t. 



t Ibid. b. % Ibid. c. § Ibid. f. 1 u. 



