1104 DIGESTIVE SYSTEM 



teeth [gl. molares], are placed outside the buccinator. The ducts of the molar glands pierce 

 this muscle near the parotid duct to open on the surface of the mucosa. 



Vessels and nerves. — The mucosa of the lips and cheeks has a characteristic reddish hue, on 

 account of the numerous blood-vessels which are visible through the thick but transparent 

 stratified squamous epithelium (figs. 849, 851) The numerous papillae of the lamina propria 

 are highly vascular. The blood-supply of the lips and cheeks is derived chiefly from the labial 

 (coronary) and buccal arteries. The rich nerve-supply (sensory) is from the infra-orbital, 

 mental and buccal branches of the fifth. The lips are especially Sensitive near the rima oris. 



Development. — During the second month in the human embryo, ledges of epithelium 

 grow into the substance of the mandibular and the fused fronto-nasal and maxillary processes. 

 These ledges develop into grooves which separate the upper and the lower lips from the upper 

 and the lower jaws, the grooves forming the oral vestibule. 



The philtrum and labial tubercle are said to correspond to the lower part of the fronto- 

 nasal process. A failure of union between the globular and the maxillary processes presents an 

 arrest of development resulting in the malformation known as "hare-lip." 



In the late foetus and newborn, the red portion of the lips consists of an external smooth 

 pars glabra, and an inner zone, pars villosa, which is covered with numerous villus-like pro- 

 jections. The largest of these reach a length of 1 mm. They also extend backward in an irregu- 

 lar band along the mucosa of the cheek. They disappear during the first few weeks of post- 

 natal life. 



In the infant, the corpus adiposum is especially well developed. On account of its supposed 

 aid as a support for the buccinator in sucking, it has been called the "sucking pad." 



The sebaceous glands of the mucosa are said not to appear until about the age of puberty. 



Variations. — As is well known, the lips and cheeks are exceedingly variable in shape, size 

 and structure in different individuals. There are also characteristic differences according to 

 race and sex in the form and structure of the lips, rima oris, beard, etc. The "hare-lip" 

 malformation was mentioned above. 



Comparative. — Typical lips are found only in mammals, and are probably organs phylo- 

 geneticaliy developed in connection with the process of suckling. 



THE PALATE 



The palate forms the roof of the mouth cavity proper, and consists of two por- 

 tions, the anterior or hard palate and the posterior or soft palate. 



The hard palate [palatum durum] (figs. 848, 852) is continuous in front and 

 laterally with the alveolar processes of the upper jaw, and gives attachment 

 posteriorly to the soft palate. It separates the mouth from the nasal cavity. It 

 is supported by the palatine process of the maxilla and the horizontal part of the 

 palate bone. The oral surface is concave from side to side, and also from before 

 backward. It is covered by a thick, somewhat pale mucosa, which is firmly 

 adherent to the periosteum through the submucosa. The submucosa contains 

 numerous mucous glands [gl. palatinse] (fig. 852), similar to those of the lips. 



In the median line of the hard palate is a line or ridge, the raphe (fig. 852) 

 terminating anteriorly in the small incisive 'papilla, which corresponds in position 

 to the bony incisive foramen. Anteriorly there occur four to six more or less 

 distinct transverse ridges [plicae palatinse transversse]. Near the posterior margin 

 of the hard palate there is on each side of the raphe a small pit (fig. 852), the 

 foveola palaiina, which is variable and inconstant. 



The soft palate [palatum molle] (figs. 848, 892) separates the posterior portion 

 of the mouth cavity from the nasal part of the pharynx. It is attached to the 

 hard palate anteriorly and to the pharyngeal wall laterally. The posterior por- 

 tion or velwn projects backward and downward into the pharynx. Its free mar- 

 gin presents a median conical projection, the uvula, and splits laterally on each 

 side to form two folds, the palatine arches, between which is located the palatine 

 tonsil (fig. 852). The palatine arches and tonsil will be described later in con- 

 nection with the pharynx. 



Structure. — The soft palate is a fold of mucous membrane enclosing a fibrous aponeurosis, 

 muscles, vessels, and nerves. It is marked in the middle line by a raphd indicating the_line of 

 junction of the two halves from which it was formed. 



The posterior layer of the mucous fold which is directed toward the cavity of the pharynx 

 is continuous with the nasal mucous meuil)rane; the anterior layer lies in the posterior boundary 

 of the mouth and is continuous with the mucous meml)rane of the hard palate. The structure 

 of the mucosa is very similar to tiiat of the lijjs (fig. 849). Mucous glands are numerous in both 

 layers, but more especially in the anterior, and make up a large portion of the mucosa and sub- 

 muco.sa (figs. 851, X')'2). 



The aponeurosis is attached above to the posterior margin of the hard palate; laterally it 

 is continuous with the aponeurotic layer of the pharyngeal wall; below, toward the lower 

 margin of the velum, it gradually disappears. It gives attachment to fibres of the levator veli 

 palatini and the jjliaryngo-palatinus (palato-pharyngeus) and to the tendon of the tensor veU 

 palatini. 



