400 



METAZOAN PHYLA 



project from the top of the head, the animal can He just under the 

 surface of the water with only its eyes and its nostrils exposed. The 

 eyes are covered with lids and both nostrils and ears possess valves which 

 may be closed when the animal is under water. 



There are several noteworthy details connected with the internal 

 anatomy. The teeth are conical, set in sockets, and are capable of 

 being shed at intervals and replaced. The tongue is flat and cannot 



iZ/na 



Radius 



Femur 

 Ilium 



Fibula 



Ischium 



Fig. 291. — Skeleton of a European turtle, Cistudo lutaria (Marsili). From a mounted 

 preparation. A, the carapace with the internal skeleton. B, the plastron, removed. 

 The limb skeletons are inside the ribs. X /^. 



be protruded, but it may be lowered and carried backward to prevent 

 water from entering the esophagus if the mouth is opened while the 

 animal is submerged. Lateral folds meet and form a palate that separates 

 the nasal chamber from the mouth and the nasal chamber becomes 

 divided by a median septum. The lungs are in a pleural cavity sepa- 

 rated from the rest of the body cavity by a diaphragm analogous to that 

 of the mammals. 



422. Testudinata. — The turtles and tortoises, which names are 

 used interchangeably, show the greatest departure from the typical 

 reptilian form. The body is inclosed in a shell (Fig. 291) consisting 



