XII.] 



MANDIBULAR AND HYOID ARCHES. 



403 



The skeletal bars of both the hyoid and mandibular 

 arches develop at first more completely than in any 

 of the other types above Fishes ; they are articulated to 

 each other above, while the pterygo-palatine bar is 

 quite distinct. 



The main features of the subsequent development 

 are undisputed, with the exception of that of the upper 

 end of the hyoid, which is still controverted. The 

 following is Parker's account for the Pig. 



The mandibular and hyoid arches are at first very 

 similar, their dorsal ends being somewhat incurved, and 

 articulating together. 



In a somewhat later stage (Fig. 136) the upper end 

 of the mandibular bar (mb), without becoming segmented 



Fig. 136. 



h.h* \h 



Embryo Pig, an inch and a third long ; Side View of 

 Mandibular and Hyoid Arches. The Main Hyoid 

 Arch is seen as displaced backwards after Segmen- 

 tation FROM THE Incus. (From Parker.) 



tg. tongue ; mk. Meckelian cartilage ; ml. body of malleus ; mh. 

 manubrium or handle of the malleus ; t.ty. tegmen tympani; 

 i. incus ; st. stapes ; i.hy. interhyal ligament ; st.h. stylohyal 

 cartilage ; h.h. hypohyal ; b.h. basibranchial ; th.h. rudiment 

 of first branchial arch ; la. facial nerve. 



262 



