450 JAMES ERNEST KINDRED 



The palatine cartilages have the same relation to the rostral 

 process of the ethmoid as before, but are longer than in the 

 younger stage and lie in a more horizontal plane — a condition 

 due to the straightening out of the anterior end of the ethmoid 

 (fig. 10). Posteriorly, the palatine cartilages have grown along 

 the fibrous strand which in the younger stage connects them with 

 the pterygoid portion of the pterygoquadrate plates. As a 

 result of this growth, the palatine cartilages and the pterygo- 

 quadrates are in closer proximity than they are in the younger 

 stage (fig. 10). 



The mandibular symphysis is broader and thicker than in 

 the 8-mm. stage and the meckelian cartilages diverge from it as 

 a pair of cartilaginous rods, w^hich thicken gradually at their 

 posterior ends to form the coronoid processes (fig. 10). The 

 mandible is now more typically teleostean than it is in the younger 

 stage, the peculiar concavity noted on the ventral surface in the 

 8-mm. stage has been obliterated. The primordium of the 

 dentary ossification appears around each Meckel's cartilage as 

 a single lamella, lateral to and separate from the cartilage. No 

 teeth are present. As in Gasterosteus, the angular process 

 projects posteriorly beyond the surface of articulation with the 

 pterygoquadrate. The pterygoquadrate articulates with the 

 dorsal surface of this portion of Meckel's cartilage at an oblique 

 angle. It becomes vertical posteriorly and there is no longer a 

 projection of the posterior end of the coronoid process dorsal 

 to it. The symplectic element extends ventral to the posterior 

 mesial region of the pterygoquadrate and the metapterygoid 

 process projecting from this region is longer than it is in the 

 8-mm. stage (fig. 10). 



Due to the straightening out of the mandible and the enlarging 

 of the oral opening, the notch present on the ventro-anterior 

 margin of the distal portion of each Meckel's cartilage has 

 disappeared. This whole region has been pushed farther ante- 

 rior than it is in the 8-mm. stage, by growth and elongation of 

 the symplectic element which has grown in concert with the 

 ethmoid cartilage. The posterior end of Meckel's cartilage no 

 longer meets the distal end of the symplectic. 



