412 CHARLES CLIFFORD MACKLIN 



the otic region to the site of the future mandibular symphysis, 

 and form by the approximation of their ventral, upturned ex- 

 tremities the apex of an angle, the sides of which enclose the 

 triangular area occupied by the structures composing the floor 

 of the mouth. In cross-section each rod is seen to be of the 

 mature type of cartilage and shows an almost uniform diam- 

 eter, although the middle of the shaft is characterized by a 

 slight but elongated spindle-shaped thickening, while the ventral 

 upturned extremity is thickened and flattened ventro-dorsally. 

 The dorsal extremity of the shaft, too, just before it becomes 

 continuous with the malleus, shows a short fusiform expansion. 



After leaving the ventro-lateral recess of the otic capsule, where 

 it is directly continuous with the malleus, the cartilage proceeds 

 forward, inward and downward, lying quite close to the pars 

 cochlearis of the otic capsule (4 mm. in the model). It then 

 changes its direction, passing almost directly forward, and only 

 slightly downward and inward, thus forming, in the portion 

 below the ala temporalis of the sphenoidal anlage, a wide curve 

 with its concavity directed outward, forward and upward. This 

 direction is maintained until the cartilage reaches a point a short 

 distance in front of its termination, when it turns rather abruptly 

 upward, and its tips become flattened, their medial edges being 

 approximated in the midline, but being separated by a thin sheet 

 of connective tissue, as is usual in homo. Thus a second curve, 

 with its concavity upward and slightly outward, is formed. 

 Upturning, enlargement and flattening of the anterior end is 

 noted by Low first in the 18 mm. stage, and is persistent, the tip 

 becoming later constricted off, and appearing in the 95 mm. 

 stage of Low as a small nodule above the symphysis. 



Excepting the small portion made up of the posterior fusiform 

 expansion the shaft is f anked laterally by the covering mem- 

 brane bone of the mandible, which also overlaps the ventral ex- 

 tremity in the manner shown in the Hertwig model, and which 

 was noted by Low as early as the 18 mm. stage. The terminal 

 upturned portion of the cartilage shows a general enlargement 

 of the cells, and to the lateral surface of this the covering bone is 

 applied very closely — indeed it would appear that this area is 

 encased by a thin plate of perichondral bone. Within this the 



