88 INTEODUCTION TO CLASSIFICATION. 



subsequent investigation seems to me, in the main, only to have 

 confirmed De Blainville's views. 



The subclass of the OENITHODELPHIA comprises those two 

 remarkable genera of Mammals, as isolated in geographical 

 distribution as in structure, OrniihorJiynchus and Echidna 

 which constitute the order Monotremata. 



In these animals the angle of the lower jaw is not inflected, 

 and the jaws are devoid of true teeth, one of the two genera only 

 (Ornithorhynchus) possessing horny plates in the place of teeth. 

 The coracoid bone extends from the scapula to the sternum, 

 with which it is articulated, as in birds and most reptiles, and, 

 as in many of the latter, there is an inter-clavicle. There is 

 no marsupial pouch, though bones wrongly termed " marsupial " 

 are connected with the pelvis. But it is to the structure of the 

 female reproductive organs that the Ornitlwdelphia owe their 

 name. The oviducts, enlarged below into uterine pouches, but 

 opening separately from one another, as in oviparous vertebrates, 

 debouch, not into a distinct vagina, but into a cloacal chamber, 

 common to the urinary and genital products and to the faeces. 

 The testes of the male are abdominal in position throughout 

 life, and the vasa deferentia open into the cloaca, and not into a 

 distinct urethral passage. The penis is indeed traversed by a 

 canal, but it is open and interrupted at the root of that 

 organ. In both sexes, the ureters pour the renal secretion, not 

 into the bladder, which is connected with the upper extremity 

 of the cloaca, but into the latter cavity itself. 



In the brain, the corpus cattosum is small, the anterior com- 

 missure large. We are but very imperfectly acquainted with 

 the reproductive processes of these animals, but it is asserted 

 that the young are devoid of a placenta. The mammary gland 

 has no nipple. 



Like the Ornitlwdelphia, the subclass DIDELPHIA contains 

 but a single order, the Marsupialia, the great majority of which, 

 like the OrniihodeJphia, inhabit Australia. They almost all 

 have the angle of the lower jaw inflected, and all possess true 

 teeth. The coracoid is, as in the higher Mammals, ankylosed 



