STRUCTURE OF CROCODILES 



713 



drowned, the Crocodilian keeps the tip of its snout above water, the 

 glottis is pushed forward to meet the posterior nares, a complete channel 

 for the passage of air is thus established, and respiration can go on un- 

 impeded. For their shore work the CrocodiHans prefer the darkness, 

 but they often float basking in the sun, with only the tip of the snout 

 and the ridge of the back exposed. 



Glands with a secretion which smells like musk are usually developed 

 on the margin of the lower jaw, at the side of the cloacal aperture, 

 and on the posterior mar 



-N.S. 



gms of the dorsal scutes. 

 The musky odour is very 

 strong during the pairing 

 season, and when the 

 animals are attacked. 



In connection with the 

 muscular system, the 

 presence of what is often 

 called an incipient dia- 

 phragm between the 

 thoracic and the abdom- 

 inal cavity is of interest. 



The brain seems very 

 small in relation to the 

 size of the skull. 



The eyes are provided 

 with a third eyehd, as 

 in most Reptiles, Birds, 

 and Mammals ; there are 

 large lachrymal glands, 

 but there is no special 

 deceitfulness about 

 " crocodile's tears." 



The ears open by hori- 

 zontal slits, over which 

 lies a flap of skin ; three 

 Eustachian passages — 

 one median and one on 

 each side — open into the 

 mouth behind the pos- 

 terior nares. -. j ■ j 

 The nostrils also can be closed, and, as we have already noticed, 

 their internal opening lies at the back of the mouth. 



The stomach suggests a bird's gizzard, for it has strong muscular 

 walls, and its pyloric end is twisted upward so as to lie near the cardiac 



part. , . 1 , • 



The heart is four-chambered, the septum between the ventricles being 

 complete, as in Birds and Mammals. But as the dorsal aorta is formed 

 from the union of a left aortic arch containing venous blood, and a 

 right aortic arch containing arterial blood, the blood which is driven to 

 many parts of the body is " mixed blood," i.e. blood partly venous, 

 partly arterial, with some of its red blood corpuscles carrying haemo. 



Fig. 422. — Cervical vertebra of crocodile. 



N.S., Neural spine; P.A., posterior articular pro- 

 cess; A. A., anterior articular process; C.R., 

 cervical rib ; C, procoelous centrum. 



