304 



DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



the parotid, submaxillan', and greater sublingual; the caudal members 

 appear to be no more than simple sprouts. Yet it is likely that when 

 older embryos are examined some slight degree of advance wall be 

 found to occur in the fourth and perhaps the fifth, the keel forma- 

 tion diminishing gradually and continuously throughout the series, 

 instead of making an absolute default at the third orbital. 



SUMMARY 



1. After the appearance of the palate process, the oral cavity may 

 be divided into three portions: the circumlingual space, the alveo- 

 lingual region, and the marginal cavity, which are, respectively, mesal, 

 ventral, and lateral to the palate process. 



The whole marginal cavity and the floor of the alveolingual region 

 are lined by a thickened epithelium. This placode, at first continuous 

 with the expansion of the cavity and in proportion to its degree, be- 

 comes resolved into sagittal strips separated by areas of thinner 

 epithelium. Thus the anlages of the salivary glands and the dental 

 ridges arise from a common placode. Caudad the lateral expansion of 

 the mouth is limited by the mandibular nerve and the quintus muscles, 

 in particular the masseter, with reference to which the marginal 

 cavity is divisible into an entomasseteric segment, where develop- 

 ment is modified and retarded, and a promasseteric segment where 

 growth is free. At the border of the muscle is a region of transi- 

 tion. 



2. The modifying effects of these relations are most pronounced 

 upon the lateral border of the mouth, the buccal sulcus, and the ad- 

 jacent portion of the marginal cavity, the maxillomandibular plane. 

 The latter is reduced in its entomasseteric portion to a blind fold or 

 flange, the orbital inclusion, which is finally separated from the oral 

 epitheUum and embedded in the mesench>Tne along the ental surface of 

 the masseter and internal pterygoid muscles. The glandular deriv- 

 atives of the plane resolve themselves into three groups, promas- 

 seteric, masseteric, and entomasseteric, comprising, respectively, the 

 parotid, the orbitoparotids, and the orbital glands. The direction 

 of their growth is also determined by the masseter, the parotid ecto- 

 masseteric, the orbitoparotids usually pro- or infra-masseteric, the 

 orbitals entomasseteric. 



