notochord and in contact with the notochord. These rods 

 are extended laterally under the otic capsules. The otic 

 capsules chondrify from anterior and posterior vestibular 

 centers. These connect with the underlying basiotic exten- 

 sion of the parachordal. The occipital arch appears behind 



several of the hypoglossal roots and at first involves two pairs 

 of centers. 



The orbital cartilage arises as a part of the pila antotica; 

 the former is perforated by the trochlear nerve and the pila 

 is not attached basally. Separate trabecular and polar car- 



orbital cartilage 



IV L^ P''° antotica otic capsule 



parachordal 



occipital arch 

 polar cartilage 



trabeculo JJ ^ I~X V-^hyor"andibula(epihyal) 



orbitonasal lamina 

 orbital carti 



palatoquodrate 



internal 



Meckel's cartilage 



occipitospinal nerve foramina 



becula 



'otoquadrate 



notochord 



prootic inctsure 



otic capsule 



B 



notochord 

 polar cartilage 



hyomandibula 

 ceratohyal 



orbitonasal lamina 



epibranchial- 



phoryngobranchial 



orbital cartilage 



procartilaginous supraorbital cartilage 



prootic incisure(Vand VII} °P*'<: pedicel 



1 _..| supraorbital foramina 



spiracular cartilage ^ 



supraorbital cartilage^ 

 occipital arch 



nasal capsule 



otic branch of VII 



palatine branch of VII 



hyomandibulor 



branch VII 



Meckel's cartilage 



orbitonasal foramen 



afferent pseudobranchia! artery 

 pituitary vein 



Figure 5-17. Development of head skeleton of Squa/us. A, lateral view of 37-mm embryo; B, C, 

 D, ventral, lateral, and dorsal views of 39-mm embryo; E, lateral view of 45-mm embryo; F, lateral 

 view of 64-mm embryo. (After El-Toubi, 1949} 



GNATHOSTOME FISHES • 121 



