MONOTREMATA. 489 



NON-PLACENTAL MAMMALS: 



CHAPTER LXXIV. 

 MONOTREMATA AND MARSUPIAL1A. 



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

 Mammalia is that of the Monotremata, constituting by itself 

 the division Ornithoddphia, 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 horny 

 plates which act as teeth. 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. The females possess no marsupial pouch, but the 

 pelvis is furnished with the so-called " marsupial bones," be- 

 lieved to be ossifications of the internal tendon of the external 

 oblique muscle 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 a flat surface 

 (Ornithorhynchus). The young are said to be destitute of a 

 placenta, or, in other words, no vascular connection is estab- 

 lished 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 supplementary 

 tarsal-bone). 



The order Monotremata includes only the two genera Orni- 



