338 THE ANATOMY OF VEKTEBRATED ANIMALS. 



The skull has a complete zygoma and well-developed pre- 

 maxillse. The lachrymal bone is large, and the lachrymal 

 foramen is situated upon the face. The tympanic bone is 

 annular, and the periotic mass so large, and enters so 

 much into the lateral walls of the skull, as to remind one 

 of its proportions in the Sauropsida. The mandible has 

 an ascending ramus. The clavicles are complete. 



The jaws are provided with teeth, the substance of which 

 is traversed by a great number of parallel vertical canals. 

 These teeth are rootless molars, and the greatest number 



8*8 



whicli has been obsei'ved is — -, but the small anterior ones 



D*D 



5 '5 



fall out, reducing them to — . The hindennost, and the 



small anterior ones, are simple cylinders, but the middle 

 teeth present a longitudinal groove, on each side. 



The submaxillary glands are very large. The stomach 

 is divided into a right and a left portion ; the former 

 having very thick and muscular walls. The intestine 

 has a coecum. It is stated that the ductus arteriosus Ion? 

 remains open. 



The two uteri open separately iato the vagina. The pla- 

 centa is deciduate and diseoidal 



d. In the Loricata, the dorsal region of the body is 

 covered by a carapace, composed of epidermal scales, and 

 of sutui-aUy united quadi-ate, or polygonal, scutes, which 

 are dermal ossifications, so that the whole structure is 

 strictly comparable to the dorsal shield of a crocodile. These 

 are the only mammals in which such scutes exist. When 

 fully developed, the dorsal armoiu* of one of these animals 

 presents five distinct shields, the edges of which permit of a 

 certain amount of motion between them. One of these 

 covers the head, and is called cephalic; another, nuclml, 

 protects the back of the neck ; a third, scapular, covers 

 the shoulders like a great cape ; a fourth, usually consisting 

 of a number of free and movable segments, covers the 

 posterior dorsal and lumbar region, as the thoraco-ab- 

 dominal shield ; and the fifth, the pelvic, is attached by its 



