AMPHIBIA 293 



and the hyoid apparatus, which remains partly cartilaginous and 

 supports the tongue. The cartilaginous cranium has a number of 

 cartilage bones and some membrane bones. 



The scapula is ossified and connected with the dorsal supra- 

 scapula, which is partly cartilaginous. The ossified coracoid has a 

 bar of cartilage, the pro-coracoid, while the clavicle is a membrane 

 bone attached to it. The coracoid and pro-coracoid are joined 

 ventrally by the epi-coracoid cartilage. 



The episternum, tipped by the cartilage plate, the omosternum, 

 projects anteriorly from the united epi-coracoids. The sternum 

 extends posteriorly and is tipped by the cartilaginous xiphisternum. 



The pectoral limb consists of the humerus, the fused radio-ulna, 

 six carpals and four complete digits with a vestigial pollex on the 

 radial side. 



The vertebral column has nine vertebrae and an elongated poste- 

 rior urostyle. The vertebral column furnishes a firm dorsal sup- 

 porting structure, and protects the delicate nerve cord. 



The pelvic arch consists of two long curved ilia, the fused ischia 

 with the ventral fused pubes. Into the acetabulum or socket fits 

 the femur. The tibia and fibula are united (tibio-fibula), while the 

 two proximal tarsal bones, the calcaneum and the astragalus, are 

 extremely elongated, making an additional segment in the hind 

 limb. Next to the three distal tarsal bones there are five well- 

 developed digits with a spur, the prehallux on the tibial side of the 

 first. 



Muscles. — In the lower Urodela the muscles are segmented in 

 both trunk and tail. In the Anura, the myotomic structure is for 

 the most part lost except in the divisions of the rectus abdominis 

 muscles. Muscles are attached to bones by means of bands of 

 modified connective tissue known as tendons. 



Physiology. Digestive System. — In the common toad, teeth are 

 absent. The retractor bulbi muscles pull the eye balls down in both 

 toads and frogs for protection, so that they are able to clamp down 

 on worms and insects that otherwise might escape from their mouth. 



When present in the Amphibia, teeth occur on the premaxillae, 

 maxillae and vomers, but they are also found on the palatines and 

 the dentaries. The tongue is fixed in many salamanders, while in 

 the frogs and toads it is usually free posteriorly and can be flipped 

 out. In a few forms, called the Aglossa, it is absent. 



