DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 205 



question not altogether simple of explanation and the data at present 

 available hardly suffice for more than a suggestion of the probable 

 nature of the process. The mandibular nerves first, and later the 

 anlages of the muscles of mastication, must be looked upon as tending 

 to confine the caudal portion of the mouth, the edge of which under- 

 goes a dorsal deflection in consequence. This entails changes in the 

 buccal sulcus, which becomes arched and at the same time acquires 

 an obhquity in the horizontal plane, on account of the lessened rate 

 of transverse growth in the caudal, as contrasted with the cranial, 

 segment of the oral cavity. When we endeavor to ascertain the 

 nature of the longitudinal growth of the mouth, and to estimate its 

 effects upon the curvature of the buccal sulcus, we enter upon more 

 debatable matter. At the outset we are confronted by the question 

 of the role played by fusion between the maxillary and mandibular 

 processes in the lengthening of the mouth. A. Pohlman has recently 

 criticized the generally accepted doctrine in an able and careful paper, 

 which is additionally important to our problems from the fact of its 

 dealing with the embryos of the cat. Pohlman points out the low 

 rehef of the various processes, the extreme shallowness of the separat- 

 ing sulci, and the absence of e\'idence of fusion in the form of epithelial 

 plates or remnants along the hues of the sulci, and argues that the 

 processes have too httle independence or individuality to be considered 

 as more than mere surface elevations, and lays stress upon their perfect 

 internal continuity with the general mesenchyme of the head. The for- 

 mation of the face he regards as the result of a subtle remodeling of the 

 embryonic material, not to be attributed to the fusion of previously dis- 

 tinct processes nor accompUshed by the obliteration of sulci. Pohlman's 

 paper is concerned mainly with the nasal field and the mesal portion 

 of the mouth ; the marginal cavity and the buccal sulcus fall outside 

 the limits of liis immediate problem. While admitting the accuracy 

 of his observations and the cogency of his general reasoning, there 

 are some facts in the development of the marginal cavity which point 

 to a different conclusion. Here the processes in question are separated 

 entally by a deep cleft, the whole maxillomandibular plane of the 

 mouth, and here also we have direct evidence of fusion between 

 the opposed processes, admittedly small in degree, in the separation of 

 the orbital inclusion {vide infra). The question naturally arises as 



