332 Henry L. Biuner 



A perfect counterpart of the structure just described we find in 

 the configuration of the upper jaw, whose surface is deeply grooved 

 for the reception of the lower jaw. The roof of this groove (sulcus 

 marginalis) is formed by the palatine processes of the maxillaria 

 and iutermaxillaria ; its outer wall, by their dentary processes, which 

 bear the teeth and are covered by the soft overhanging lip; its 

 inner boundary, by a membranous fold which separates it from the 

 oral cavity. The sulcus marginalis extends around the entire margin 

 of the upper jaw, deepening gradually from the angle of the mouth 

 toward the rostrum, where it presents in the middle line a pit-like 

 depression, the fossa subrostralis media (Fig. 10, PL XVII), which 

 serves for the reception of the tuberculum praelinguale. On each 

 side of the fossa is a cushion like elevation, pulvinar subrostrale 

 {P.S.), which is richly glandular and corresponds on each side to a 

 fossa praelingualis. Lateral from each pulvinar subrostrale lies still 

 another depression (fossa subrostralis lateralis), which serves for the 

 reception of the anterior end of the longer segment of the dentale. 



b. Description of a new Muscle in the upper Lip. 



The observations recorded above are for the most part simply 

 a confirmation of work already done by Gaupp (20) and Holl (28). 

 In these earlier descriptions, however, the structure and function of 

 the upper lip has received little or no attention. This lip (Figs. 9 

 and 10, PI. XVII and Figs. 11 and 12, PI. XVIII) is a thickened 

 duplicature of the skin, which begins as a low fold at the angles of 

 the mouth and increases gradually in depth towards the rostrum; it 

 thus assists in forming the outer boundary of the sulcus marginalis. 

 The outer layer of the lip is directly continuous with the external skin 

 and, like it, is richly supplied with glands, which decrease somewhat 

 in size toward the margin of the lip. The inner layer of the lip is 

 glandless, unpigmented and thinner than the outer layer. Between 

 these two layers in the upper region of the lip lies the tooth-bearing 

 margin of the dentary processes of the maxillaria and intermaxillaria. 

 The teeth themselves are all more or less imbedded in the inner 

 layer of the lip, the functional teeth having only their crowns ex- 

 posed. Below and outside of the teeth the lip hangs as a free fold, 

 which lies in contact with the outer inferior surface of the lower 

 jaw when the mouth is closed. The epithelial covering of the lip 

 is a stratified pavement variety, which also lines the sulcus marginalis; 



