CAVITY OF THE NOSE. 133 



The LIPS surround the opening of the mouth ; they consist chiefly of the 

 fleshy part of the orbicularis oris muscle, covered externally by integu- 

 rnent, and internally by mucous membrane. The lower lip is the larger 

 and more movable of the two. Between the muscular structure and the 

 mucous covering lie the labial glands ; and in the substance of each lip, 

 nearer the inner than the outer surface, and at the line of junction of the 

 two parts of the orbicularis, is placed the arch of the coronary artery. 



TEETH. In the adult there are sixteen teeth in each jaw, which are 

 set in the alveolar borders in the form of an arch, and are surrounded by 

 the gums. Each dental arch has its convexity turned forwards ; and, 

 commonly, the arch in the maxilla overhangs that in the mandible when 

 the jaws are in contact. The teeth are similar in the half of each jaw, 

 and have received the following names : the most anterior two are incisors, 

 and the one next behind is the canine tooth ; two, still farther back, are 

 the bicuspids ; and the last three are molar teeth. Moreover, the last 

 molar tooth has been called also " dens sapientire," from the late period of 

 its appearance. The names applied to the teeth indicate very nearly the 

 part they perform in mastication ; thus the incisor and canine teeth act as 

 dividers of the food, whilst the bicuspid and molar teeth serve to grind 

 the aliment. 



The several parts of the teeth, viz., the crown, fang, and neck ; the 

 general and special characters of those parts in the different groups of 

 teeth ; and the structure of the different components of a tooth, must be 

 referred to in some general treatise on anatomy. 



SECTION XIII. 



DISSECTION OF THE NOSE. 



To obtain a view of the interior of the nose, it will be necessary to make 

 a longitudinal section through the base of the skull. Whilst the student 

 is examining the boundaries of the nose he will derive advantage from the 

 use of a vertical section of a dried nasal cavity. 



Dissection. Before sawing the bone, the loose part of the lower jaw 

 on the right side should be taken away ; further, the tongue, hyoid bone, 

 and larynx, all united, may be detached from the opposite half of the lower 

 jaw, and laid aside till the dissector is ready to use them. 



On the right side of the middle line saw through the frontal and nasal 

 bones, the Cribriform plate of the ethmoid, and part of the body of the 

 sphenoid bone, without letting the saw descend into the nasal cavity. 



Next the roof of the mouth is to be turned upwards, and the soft parts 

 are to be divided on the right of the median line opposite the cut in the 

 roof of the nose. The saw is then to be carried through the floor of the 

 nose and the body of the sphenoid bone in such a direction as to come 

 into the incision above. 



The piece of the skull is now separated into two parts, right and left ; 

 the right half will serve for the examination of the meattises, and the left 

 will show the septum nasi, after the mucous membrane has been removed. 



The CAVITY OF THE NOSE is placed in the centre of the bones of the 

 face, being situate above the mouth, below the cranium, and between the 



