1200 



THE ORGANS OF DIGESTION 



is stratified and ciliated. 1 Beneath the mucous membrane on the oral surface of the soft palate is 

 a considerable amount of lymphoid tissue. The palatine glands form a continuous layer on the 

 pharyngeal surface and around the uvula. 



The arteries supplying the palate are the descending palatine branch of the internal maxil- 

 lary artery (a. palatina descendens), the ascending or palatine branch of the facial artery 

 (a. palatina ascendens), and sometimes a palatine branch of the ascending pharyngeal. The 

 veins terminate chiefly in the pterygoid and tonsillar plexuses. The lymphatic vessels pass 

 to the deep cervical nodes. 



Development of the Mouth. The mouth is developed partly from the stomodeum, the 

 depression between the head end of the embryo and the pericardial area, and partly from the 

 floor of the extreme end of the foregut. The floor of the stomodeum is the thin, buccopharyngeal 

 membrane, formed by the apposition of ectoderm and entoderm; this membrane wholly disap- 

 pears after the second week of embryonic life, and a communication is established between the 

 mouth and future pharynx. With the development of the face the nasal passages are separated 

 from the mouth proper by the coalescence of the maxillary and palatal processes of the first 

 visceral arch with the lateral nasal and globular processes forming the maxillae and palate. 



The development of the teeth is described on page 1214. 



Applied Anatomy. Cleft palate is 'by no means a rare congenital deformity, and may be 

 partial or complete. Most of the cleft is in the middle line. It may be a mere cleft of the 

 uvula, it may be limited to the soft palate, or it may involve the hard palate to but not include 

 the alveolus. It may pass through the alveolus, but if it does so it ceases to be median at this 

 point, and follows the line of suture between the incisive bone and the maxilla (pp. 106 and 

 152). Complete cleft palate is likely to be accompanied by harelip. This cleft in the lip is 

 not median, but is at the termination of the palate cleft. If the cleft of a cleft palate runs 

 along each side of the incisive bone, the bone is isolated from the maxilla and the cleft is 

 Y-shaped. In such a case double harelip is present. 



The Teeth (denies). The human subject is provided with two sets of teeth, 

 which make their appearance at different periods of life. 



Those of the first set appear in childhood, and are called the temporary, decidu- 

 ous, or milk teeth. Those of the second set are named permanent or succedaneous 

 teeth. 



The temporary teeth are twenty in number four incisors, two canines, and four 

 molars in each jaw (Figs. 910 and 933). 



The permanent teeth are thirty-two in number four incisors (two central and 

 two lateral), two canines, four bicuspids, and six molars in each jaw (Figs. 918 and 

 922). 



The dental formulae may be represented as follows: 



Temporary Teeth. 



Total, 20. 



Permanent Teeth. 



Incisor. Canine. Bicuspid. Molar. 



1 



Total, 32. 



General Characters (Fig. 923). Each tooth consists of three portions the 

 crown or body (corona dentis), projecting above the gums; the root or fang (radix 

 dentis), entirely concealed within the alveolus; and the neck (collum dentis), the 

 constricted portion between the root and crown, covered by the gum. 



The roots of the teeth are firmly implanted within the sockets or alveoli of the 

 jaws (alveoli dentales) (see pp. 104 and 117). These depressions are lined with 

 periosteum, which is reflected on to the tooth at the apex of the root and covers 



1 According to Klein, the mucous membrane on the nasal surface of the soft palate in the fetus is covered 

 throughout by columnar ciliated epithelium, which subsequently becomes squamous; and soms anatomists 

 state that it is covered with columnar ciliated epithelium, except at its free margin, throughout life. 



