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NON-PLACENTAL MAMMALS. 



CHAPTER LXIX. 

 MONOTREMATA AND MARSUPIALIA. 



ORDER I. MONOTREMATA. The first and lowest order of the 

 Mammalia is that of the Monotremata, constituting by itself 

 the division Ornithodelphia, and containing only two genera, 

 both belonging to Australia namely, the Duck-mole (Ornitho- 

 rhynchus} and the Porcupine Ant-eater (Echidna). 



The order is distinguished by the following characters : 

 The intestine opens into a " cloaca" which receives also the 

 products of the urinary and generative organs, which discharge 

 themselves into a urogenital canal the condition of parts being 

 very much the same as in Birds. The jaws are either wholly 

 destitute of teeth (Echidna) or are furnished with four horny 

 plates which act as teeth (Ornithorhynchus). The pectoral arch 

 has some highly bird-like characters, the most important of these 

 being the extension of the coracoid bones to the anterior end of the 

 sternum. An inter clavicle is also present. The females possess 

 no marsupial pouch, but the pelvis is furnished with the so-called 

 "marsupial bones" being special ossifications of the internal 

 tendons of the external oblique muscles of the abdomen. The 

 testes of the male are abdominal throughout life, and there is 

 therefore no scrotum, whilst the vasa deferentia open into the 

 cloaca. The corpus callosum is very small, and has been 

 asserted to be altogether wanting. There are no external 

 ears. The mammary glands have no nipples, and their ducts 

 open either into a kind of integumentary pouch (Echidna) or 

 simply on aflat surface (Ornithorhynchus). The young are said 

 to be destitute of a placenta, or, in other words, no vascular con- 

 nection is established between the foetus and the mother. The feet 

 have five toes each, armed with claws, and the males carry 

 perforated spurs on the back of the tarsus (attached to a sup- 

 plementary tarsal bone). 



The order Monotremata includes only the two genera Orni- 



