256 PROCEEDINGS OF THE ACADEMY OF [1888. 



the sutural ruga. The sutural ruga is the widest of any in the 

 entire series. It is usually inclined somewhat backward, but never 

 forward. A deep sulcus is often seen at the base of the sutural fold 

 anteriorily. 



The sutural fold divides the hard palate into two parts, the pre- 

 sutural and the post-sutural. The pre-sutural space thus answers to 

 the premaxilla and has but one ruga^ (see fig. 2). The post-sutural 

 space has four to seven rugse and are named in order from before 

 backward the first, second, third, fourth, etc. Of these folds the third 

 is the best developed. As a rule the first and the second are the 

 least so and are represented usually by small nodules, or by groups 

 of papules, at the outer portion of the vault. They are often aborted. 

 The fifth, sixth, and seventh are also often aborted or represented by 

 faintly expressed broken sinuate lines. The presutural portion of 

 the vault is nearly flat and is of a special use in presenting a firm 

 surface for the tip of the tongue to press against in mastication and 

 in speech. The post-sutural space is concave with an abrupt declivity 

 forwards. The alveolar processes of the molar range and the declivity 

 named bound tlie true palatal vault. It presents extraordinary 

 varieties, no two subjects being in all respects the same. 



The pre-sutural rugse were found in an examination of 90 ex- 

 amples of hard palates, present on the right side alone in 11, on 

 the left side alone in 1, on both sides, 17, absent in 50, doubtful in 

 11. Occasionally a system of minute raised folds extends from the 

 raphe outward in the spaces between the rugne. 



The roof of the mouth at the region of the incisors and the bicus- 

 pids is distinguished from that of the molars by the presence of folds 

 of gum-tissue placed at the necks of the teeth. These may receive 

 the names of the neck-folds. They indicate a disposition of the 

 mucous membrane to be in excess at the parts where the palate is 

 the narrowest. They often entirely occupy the pre-sutural space. 

 The rugte as a whole, are the best developed in the regions where 

 the neck-folds are found. 



Each palatal ruga is divided into a median and a lateral part. 

 The median part, as a rule, is crescentic in outline with the convex- 

 ity directed forwards. The lateral is directed forwards. Taken 

 together the last named folds are arranged in vertical series, (i. e. with 

 the main axes of the crowns of the teeth) and are either separated by 



1 Some of the figures show neck-folds which must not be confounded with rugae. 



