XIII 



PHYLUM CHORDATA 479 



incisors large, the canines usually small or absent ; the molars 

 blunt, with tubercles or transverse ridges. 



This order includes the Wombats (Phascolomyidce), the Phalan- 

 gers (Phalangeridce), and the Kangaroos (Macropodidce]. 



SECTION B. EUTHERIA. 



Theria in which a marsupium is absent, and the young are always 

 nourished in utero, for a considerable period, through the agency 

 of a placenta. The anus and urinogenital aperture are usually 

 not surrounded by a common sphincter. The alisphenoid never 

 contributes to the formation of the wall of the tympanic cavity ; 

 except in the Hyracoidea and some Rodents, the jugal takes no 

 part in bounding the glenoid cavity ; and there are no marsupial 

 bones. A corpus caliosum is present. 



ORDER 1. EDENTATA. 



Eutheria, in which the teeth are absent in the adult or the 

 dentition is imperfect, incisors and canines being seldom repre- 

 sented ; and, though there may be numerous premolars and molars, 

 these never form roots and are devoid of enamel. All, with the 

 exception of two genera, are monophyodont. The sacral vertebrae 

 are frequently in excess of the number usual in other orders. The 

 coracoid process is usually relatively larger than in other Eutheria, 

 and may not become completely fused with the scapula. The 

 brain is sometimes of low, sometimes of comparatively high 

 organisation. The placenta is deciduate or non-deciduate, diffuse, 

 zonary, or discoidal (vide infra). 



There are five families comprised in the order, each characterised 

 by the presence of a number of remarkable and peculiar features : 

 viz., the Sloths (BTadypodidce) , the American Anteaters (Myrviie- 

 copliagidce), the Armadillos (Dasypodidce), the Scaly Anteaters 

 (Manidce), and the Cape Anteaters (Orycteropodidai). 



ORDER 2. CETACEA. 



Aquatic Eutheria with large head, fish-like, fusiform body, 

 devoid of hairy covering, with the pectoral limbs paddle-like, the 

 pelvic limbs absent, and with a horizontal caudal fin. A vertical 

 dorsal fin is usually present. There is a long snout, and the 

 nostrils open by two lateral external apertures or a single median 

 one, situated in all the recent forms far back towards the summit 

 of the head. The cervical region of the spinal column is very 

 short, and its vertebrae usually completely united together. 

 Clavicles are absent. The humerus is freely movable at the 

 shoulder, but all the other articulations of the limb are imperfect. 



