306 THE DEVELOPMENT OF THE CHICK 



sets in about the eighth day, and the early thickening of the 

 epithelium of this part already referred to is undoubtedly the 

 first stage in the process. 



The development of the musculature of the tongue has not 

 been followed. The development of the skeletal parts is con- 

 sidered under the head of the skeleton. 



Oral Glands. The following oral glands occur in the hen: 

 1, lingual glands; 2, mandibular glands.; 3, glands opening at 

 the angle of the mouth; 4, palatine glands in the neighborhood 

 of the choanse. The only account of their development known 

 to me is the brief one of Reichel. All the glands begin as solid 

 ingrowths of the mucosa, which may branch more or less, and 

 secondarily acquire a lumen. Their development begins relatively 

 late. The mandibular glands appear first on the eighth day as 

 a series of solid ingrowths of the mucosa extending on both sides 

 of the base of the tongue forward to near the mandibular sym- 

 physis. They are still mostly solid on the eleventh day, and 

 very slightly branched, if at all. The lingual glands arise beneath 

 the lateral margin of the tongue and grow up on each side of the 

 lingual cartilage towards the upper surface where they branch 

 out. They begin to form on the eleventh day. No glands form 

 on the upper surface of the tongue. The glands of the angle of 

 the mouth appear on the eleventh day, in situ, as slight epithelial 

 ingrowths. Their further history has not been followed. An- 

 terior and posterior palatine glands can be distinguished; the 

 first in front of the choanae, the latter at the sides of and behind 

 the choanse. They begin to appear after the eleventh day. 



II. DERIVATIVES OF THE EMBRYONIC PHARYNX 

 The pharynx, which is such an extensive and important region 

 of the early embryo owing to the development of the visceral 

 arches and clefts, becomes relatively much reduced in the process 

 of development, though of course it becomes much larger abso- 

 lutely. In the adult it is a somewhat ill-defined cavity from 

 which the oesophagus leads away posteriorly, and which is con- 

 fluent with the mouth anteriorly. The tubal fissure opens in 

 its roof and the glottis in its floor. During the course of develop- 

 ment, however, certain more or less persistent structures form 

 from its walls, or from the epithelium of the pouches. Although 

 these are relatively inconspicuous organs in the adult, they are of 



