THE SKELETAL SYSTEM 617 



region of the pharynx between the hyoid and the first branchial, and 

 connects the ventral ends of both these arches. 



The hypo-branchial plate consists of the lower ends of the first 

 branchials which have become flattened and expanded. The ventral 

 ends of the other three branchials fuse with the hypo-branchial plate. 



The cerato-branchials are the lateral and mid- 



u 



die sections of the branchial cartilages between the 

 visceral pouches which remain separate from one 

 another. 



At metamorphosis, when the gill slits close, 

 many changes naturally must take place in the 

 Fig. 354. structures just described. For example, the hyoid 



archX id of an l 29 an mm! bar loses its connection with the palato-quadrate, 

 tral* v f iew'. iU bb" Basl- an( ^ Decomes smaller in diameter, while the copula 

 5a^ ch w? ( basihyai^ c ch likewise becomes smaller and a pair of new car- 



ceratohyal; ho hypo- tilagCS develop On each side of it, which then COn- 

 branchial plate ; 1-4, first 



nect t ^ ie hypo-branchial plate with the hyoid por- 

 tions. These are the manubrial cartilages. 



The hyo-branchial apparatus of an adult frog is made up of a broad 

 median plate of cartilage which has been formed by the fusion of 

 manubrium, copula, and hypo-branchial plate. The hyoid cartilages re- 

 main as slender processes called the hyoid cornua. The remaining por- 

 tions practically disappear. 



The membrane bones. In those portions of the cranium where con- 

 siderable stretching has taken place, such as in the roof of the skull and 

 the lining of the mouth, the substance is thinner than in the cartilaginous 

 portions, and is then called membrane. 



Membrane is nothing more than stretched-out-cartilage. 



The Parasphenoid. This is a single median bone, and tne first 01 

 all bones of the skull to appear, whether cartilaginous or membranous. 

 It forms in the roof of the mouth when the tadpole is about twenty 

 millimeters long. The parasphenoid becomes dagger-shaped and covers 

 the entire basicranial fontanelle. 



The frontals and parietals, which are paired, appear later and cover 

 the supracranial fontanelle. They later fuse to form the fronto-parietals. 



The nasals form the roof of the olfactory capsules and the septo- 

 nasals or intra-nasals appear within the capsules. 



The premaxillae and maxillae are the membranous parts which be- 

 come the margins of the upper jaw. 



The dentary and angular cartilages surround Meckel's cartilage ; 

 the dentary connects with the infra-rostrals of Meckel's cartilage. 



The vomers are paired, and appear beneath the olfactory capsules. 



The palatines form across the anterior margins of the orbits. 



