PRACTICAL CONSIDERATIONS: THE MOUTH. 1589 



certain well-developed alveoli filled with large mucous cells, or they may be present 

 in considerable numbers. Mucous cells are much less numerous in the sublingual 

 glands of young infants than in the adult organ. The relatively wide lumen of the 

 alveoli and the more reticulated appearance of their epithelium serve to distinguish 

 the exhausted sublingual gland from the parotid of similar condition. 



The normal secretions of the oral glands, mucous as well as serous, contain no 

 formed elements ; occasionally accidental granules or cell remains are present. The 

 characteristic spherical so-called salivary corpuscles which occur in varying numbers 

 in the mixed oral secretion have no relation to the salivary glands, since they are 

 only modified leucocytes escaped from the lymphoid tissue of the faucial and lingual 

 tonsils. On gaining the oral cavity, these cells are affected by the saliva and become 

 greatly swollen, the granular remains of their cytoplasm exhibiting molecular motion 

 in a marked degree. 



Development of the Oral Glands. — The earliest traces of the salivary 

 glands are seen during the second foetal month. The anlage for the submaxillary 

 gland first appears about the sixth week ; next that for the parotid about the 

 eighth week ; a little later that for the sublingual. The parotid anlage develops 

 from the oral ectoblast along the lateral groove separating the upper and lower jaws. 

 The submaxillary and sublingual glands arise from a ridge-like anlage of the buccal 

 epithelium occupying the furrow marking the angle between the tongue and the floor 

 of the mouth, the anlage for the sublingual lying nearer the tip of the tongue. At 

 first the parotid and submaxillary lie about equally removed from the oral opening, 

 but later migration occurs, the former passing backward and the latter forward. 



The development of the gland in each case begins as a solid cylindrical out- 

 growth from the deeper layer of the oral epithelium, which presents a local thicken- 

 ing. The cylinder rapidly lengthens and branches, so that by the eighth or tenth 

 week the submaxillary and parotid glands respectively consist of a main stalk and 

 terminal buds. The anlage of the sublingual gland gives of? epithelial buds on 

 acquiring a length of about i mm. The primary sprouts of the anlage subdivide and 

 eventually become the smaller ducts and the glandular tissue. Meanwhile the imme- 

 diately surrounding mesoblast undergoes condensation, and contributes the connecti\e- 

 tissue envelope with its prolongations between the lobules and acini supporting the 

 blood-vessels and nerves. Towards the close of the third month, while the gland- 

 tubules are still solid, the lumen of the future main excretory duct appears in the 

 epithelial cylinder, extending from the free surface towards the alveoli. The latter 

 acquire their lumen during the fifth month. 



The smaller oral glands, including those of the lips, cheeks, tongue, and palate, 

 develop much later than the larger salivary, since their anlages appear during the 

 fourth month. The details of their development correspond in general with those 

 attending the formation of the larger oral glands. 



PRACTICAL CONSIDERATIONS : THE MOUTH. 



The chief congenital deformities of the mouth are harelip and cleft palate. 

 Harelip results from a failure of the developmental procedures concerned in forming 

 and differentiating the nasal and buccal cavities. These processes have already been 

 described in connection with the formation of the face (page 59). L^pon the down- 

 growth of the fronto-nasal process depends the formation of the vomer, the perpen- 

 dicular plate of the ethmoid and the external nose, and of the intermaxillary bone 

 and that portion of the upper lip corresponding to the four incisors. The partition 

 separating the nasal from the oral ckvity, later the hard and soft palates, is formed 

 by the union of the horizontal palatal plates from the buccal aspect of the two maxillary 

 processes (Fig. 76). When the frontal and maxillary processes fail to unite on one 

 side, single harelip results, the cleft in one side of the lip lying opposite the space 

 between the upper canine and lateral incisor, or between the latter and the central 

 inci.sor. When union between the maxillary and the frontal processes fails on both 

 sides, double harelip follows, the lateral incisors often being absent and the inter- 

 maxillary bone with the central incisors and the median portion of the lip occupying 

 a position beneath the nasal septum. 



