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Sub-Class Prototheria (Monotremes). 



Slate briefly the Chief Distinctive Characters of the Prototheria (Mono- 

 tremes). Give examples, and mention their Distribution. 

 * cf. Reptiles. f cf. Birds. 



Vertebrae without epiphyses*t. Odontoid process is at first 

 separate from axis. Skull bones ankylosed (sutures obliterated).f 

 Without teeth (except young Ornithorhynchus). Shoulder girdle 

 like that of lizards* ; coracoids well developed and articulated with 

 sternum, clavicles beneath preooracoids and closely applied to a 

 T-shaped interclavicle. Epipubio bones on pubes. Acetabulum 

 incompletely ossifiedf (Echidna}. A tarsal spur, containing the duct 

 of a gland. A large anterior commissure ; corpus callosum small or 

 absent. A cloaca*|. The right auriculo-ventricular valve partly 

 muscular f (Ornithoryhnchus). Testes within abdomen. Genital 

 ducts, ureters, and bladder open separately into urinogenital finus. 

 Penis beneath ventral wall of cloaca, and protruding from it behind. 

 Right ovary small and not functionalf. Oviducts large, without 

 distinct regions, and separatef. Ova large with tough shells (seg- 

 mentation meroblastio)*f. Oviparous*f (Echidna carries egg in a 

 ventral skin pouch of the abdomen). The young, when hatched, 

 receive milk from the mother ; mammary glands (without mammae 

 or teats) open into slight depressions. 



Ornithorhynchus (The Duckmole). East and South Australia, and 

 Tasmania. Burrows in banks of lakes and rivers. Is semi-aquatio ; 

 its fore-feet (with claws) are webbed, and its flattened jaws (with 

 horny plates), covered with skin, form a large duck-bill. Mode of 

 feeding, duck-like. Fur short and soft, eyes small, tail flat. 



Echidna (The Spiny Ant-eater). East Australia, Tasmania, 

 New Guinea. Nocturnal. Burrowing. Snout slender and tubular. 

 Covered with stout spines amidst hair. 



Proechidna. New Guinea. 



Sub-Class Metatheria (Marsupials). 



Mention the Principal Characteristic Features of the Metatheria 

 (Marsupials). 



Angle of lower jaw (i.e., lower posterior end of jaw) is inflected. 

 Only one functional set of teeth (monophyodont) ; more incisors 

 on the upper than on the lower jaw, and number (for each side) 

 may exceed three. Precoracoids are small processes of scapula. 

 Pubes generally bear epipubic bones (sesamoids). A large anterior 

 commissure ; corpus callosum small or absent. The ureters open 

 into the bladder. Anus usually situated well within the urinogenital 

 sinus (" cloaca "), and one sphincter muscle surrounding both open- 

 ings. Scrotum in front of the penis. Two uteri and two vaginae ; 

 upper portions of vaginae frequently united, and at junction a vaginal 



