xni 



PHYLUM CHORDATA 



459 



the rest grooved longitudinally on the outer side and with two 

 transverse grooves, bounded by ridges, on their crowns. The 

 first pre-molar of the lower jaw has two grooves and three ridges ; 

 the second is similar to those of the upper jaw. Behind the pre- 

 molars are the molars, three on each side both in the upper and 

 lower jaws. These are similar to the upper pre-molars, except the 

 last, which is small and of simple shape. 



Opening into the cavity of the mouth, or huccal cavity, are the 

 ducts of four pairs of salivary glands — \\iQ parotid, the infraorbital, 

 the mbmaxillary (Fig. 1 088, s. mx. gl.), and the sublingual (s. gl.). 

 On the floor of the mouth is the muscular tongue, covered with 

 a mucous membrane which is beset with many papillee, on certain 

 of which the taste-buds (p. 108) are situated. The roof of the 

 mouth is formed by the hard palate, which is crossed by a series 

 of transverse ridges of 



its mucous menibrane. sept.oart 



Posteriorly the hard 

 palate passes into the 

 soft palate, which ends 

 behind in a free pen- 

 dulous flap in front of 

 the opening of the 

 posterior nares. At the 

 anterior end of the 

 palate is a pair of 

 openings — the naso- 

 palatine or anterior 

 palatine canals, leading 

 into the nasal cham- 

 bers, and into them 

 open a pair of tubular 

 structures — the organs 

 of Jacdbson {¥\g. 1087, 

 jcb) — enclosed in car- 

 tilage atid situated on 

 the floor of the nasal 

 cavities. Behind the 

 mouth or buccal cavity 

 proper is the pharyno;, 

 which in the Rabbit 

 is not sharply marked 

 off from the buccal 



cavity, but begins where the hard palate' ends. The pharynx is 

 divided into two parts, an upper or nasal division, and a lower 

 or bvAxal division, by the soft palate. The passage of the pos- 

 terior nares is continuous with the nasal division, at the sides 

 of which are the openings of the Eustachian tubes. The nasal 



F F 2 



Ic/rdct- 



n.eia.pcil 



Fig. 1087.— lepus cuniculUB. Vortical section tlirougli 

 the anterior part of the nasal region of tlie head. inc. 

 section of larger incisor tooth ; jci*. lumen of Jacobson's 

 oi-gan, surrounded by cartilage ; Ut. del. lacrymal duct ; 

 max. maxilla ; max. trb. maxillary turbinate ; nas. nasal 

 ijone ; nas. pal. naso-palatine canal ; sept. cart, cartilagin- 

 ous nasal septum. (After Krause.) 



