THE PERCH 217 



gether with certain other bones, form the skeleton of the upper 

 jaw, the roof of the mouth, and the lower jaw. The second vis- 

 ceral arch is the hyoid arch, the dorsal half of which enters into 

 relation with the mandibular arch and becomes the suspensorium 

 of the jaws, — that is, the connecting link between them and the 

 cranium, — and the ventral half of which forms the support of 

 the tongue and bears the opercular bones and the branchioste- 

 gal rays. 



The Mandibular Arch. Identify the following bones forming 

 the lower jaw, the ventral half of this arch. At its proximal end 

 is the large articular bone, by means of which it articulates with 

 the quadrate bone of the upper jaw. The forward and middle 

 surfaces of the lower jaw are formed on each side by the large 

 dentary bone, which bears teeth. A small additional bone, the 

 angular, is present at the hinder end of the jaw. 



Identify the bones of the upper jaw. Forming the forward end 

 and the lateral margins of this jaw are two pairs of bones, the 

 premaxillae and the maxillae. The former bear teeth and meet 

 each other in the middle Hne in front; the latter are without 

 teeth, being a pair of flattened rods back of the premaxillae, with 

 which their anterior ends articulate. 



The hinder end of the upper jaw is made up of a series of paired 

 bones. The quadrate bone is a large, triangular bone at the hinder 

 end of the upper jaw on each side, with which the lower jaw ar- 

 ticulates. The metapterygoid is a large bone lying just above the 

 quadrate and back of the orbit. The ectopterygoid is an elongated 

 bone which projects in front of the quadrate. The endopterygoid 

 is a thin plate above the anterior end of the ectopterygoid and 

 forming a part of the roof of the mouth. In front of the last two 

 bones is the palatine, which helps form the roof of the mouth and 

 bears teeth. 



Surrounding the orbit and forming its margin on all except the 

 dorsal side is a row of bones called the suborbitals, which are very 

 easily lost in the cleaning. The most anterior one is a large bone 

 between the orbit and the maxilla, on the surface of which will 

 be seen radiating canals belonging to the lateral-line system of 

 sensory canals* 



