ORGAN OF SMELL IN MAMMALIA. 213 



extends, beneath it, along about three-fourths of the lower third 

 of the septum, but subsides to a point ; the major part of the 

 septum is gristly. 



In the Hippopotamus the nostrils are relatively small, promi- 

 nent, wide apart, and are served by muscles which open and 

 close them like the eyelids, besides protruding and retracting 

 them. The accessory sinuses of the nasal chamber are very 

 little developed. Their extent and size offer a great contrast in 

 the Hog-tribe, in which the essential parts of the olfactory organ 

 are also relatively larger and more complex. The rhinencepha- 

 lon is large, with many nerves, and the cribriform plate of great 

 extent : the ' labyrinthic ' part of the capsule attached to its 

 under or outer surface forms nine or ten longitudinal, slightly 

 diverging folds, fig. 153, q, the three or four uppermost of which 

 coalesce to form the ethmoturbinal, which is long, slender, 

 subconvolute, and attenuated to a fine point forward, ib. s. 

 This figure gives an oblique view of the e labyrinth,' q, and 

 ethmoturbinal, s, of the right and left sides. The nasoturbinal 

 is of moderate length. The somewhat deeper and more con- 

 volute f maxilloturbinal ' is shown at p : the accessory ( nasopa- 

 latine ' fossa, at k. The pterygoid, f, bounding the posterior nasal 

 opening is excavated and expanded above by a sinus continuous 

 with those of the sphenoid, ?i. The accessory sinuses of the 

 nasal chamber are very considerable in the Hog-tribe : the 

 frontal ones (vol. ii. p. 468, fig. 315, 11, young Pig) extend back- 

 ward over the calvarium to the occiput in the Boar: a structure 

 well shown in the Babyroussa, No. 3346, * in which preparation 

 the extension of the sphenoidal sinus (ib. fig. 315, f) into the 

 base of the pterygoid is demonstrated, where it is divided into 

 an external and internal compartment. In Phacochcerus the 

 pterygo-nasal fossa is simple, and the frontal are almost separated 

 from the parietal sinuses by the near approximation of the inner 

 to the outer table of the skull. The pterygo-nasal fossa? are 

 absent in Dicotyles. In all Suidce. the external nose is somewhat 

 prolonged and truncate, the nostrils opening upon a naked disc : 

 the cartilages of the nose form a complete tube, which is a con- 

 tinuation of the bony nostrils, and near the end of the snout 

 the cartilaginous septum becomes ossified, and forms the prenasal 

 ossicle (ib. fig. 315, o). 



In the Ox the cribriform plate is relatively smaller and the 

 olfactory nerves fewer than in the Horse : the labyrinthic part of 

 the ethmoid consists of about six short narrow longitudinal 



1 XLIV. p. 557. 



