I860.] Cerebral System of the Class Mammalia, 179 



plantigrade, and pentadactyle, and they have complete clavicles. 

 Like Rodents, they are periodical testiconda, and have large prostatic 

 and vesicular glands : like most other Lissencfphala, the Insectivora 

 have a discoid or cup-shaped placenta. They do not exist in South 

 America and Australia ; their office in these continents is fulfilled by 

 Marsupialia : but true Insectivora abound in all the other continents 

 and their contiguous islands. 



The order Cheiroptera, with the exception of the modification 

 of their digits for supporting the large webs that serve as wings, 

 repeat the chief characters of the Insectivora : a few, however, of 

 the larger species are frugivorous and have corresponding modifications 

 of the teeth and stomach. The mammae are pectoral in position. 



The most remarkable examples of periodically torpid Mammals 

 are to be found in the terrestrial and volant Insectivora. The frugi- 

 vorous Bats differ much in dentition from the true Cheiroptera, and 

 would seem to conduct through the Colugos or Flying Lemurs, 

 directly to the Quadrumanous order, from which, in Buffon*s 

 hypothesis of degeneration, they might be derivatives. The Chei- 

 roptera are cosmopolitan. 



The order Bruta, called Edentata by Cuvier, includes two genera 

 {Myrmecophaga and Manis) which are devoid of teeth ; the rest 

 possess those organs, which, however, have no true enamel, no fangs 

 or roots, are never displaced by a second series, and are very rarely 

 implanted in the premaxillary bones. All the species have very long 

 and strong claws. The ischium as well as the ilium unites with the 

 sacrum ; the orbit is not divided from the temporal fossa. The Three- 

 toed Sloths {Bradypus) manifest their affinity to the oviparous 

 Vertebrata by the supernumerary cervical vertebrae supporting false 

 ribs and by the convolution of the windpipe in the thorax ; and the 

 unusual number — three and twenty pairs — of ribs, forming a very 

 long dorsal, with a short lumbar, region of the spine, in the Two-toed 

 Sloth (C/io/tepz^), recalls a lacertine structure. The same tendency 

 to an inferior type is shown by the abdominal testes, the single cloaca! 

 outlet, the low cerebral development, the absence of medullary canals 

 in the long bon|j^ in the Sloths, and by the great tenacity of life and 

 long-enduring irritability of the muscular fibre, in both the Sloths and 

 Ant-eaters. 



The order Bruta is but scantily represented at the present period. 

 One genus, Manis or Pangolin, is common to Asia and Africa ; the 

 Orycteropus is peculiar to South Africa ; the rest of the order, con- 

 sisting of the genera Myrmecophaga, or true Anteaters, Dasypus or 

 Armadillos, and Bradypus or Sloths, are confined to South America. 



Having defined the orders into which the Lissencephala were sub- 

 divided, the speaker adduced his evidences of the more truly natural 

 character, notwithstanding the differences of form, structure, and habits, 

 of this primary group, than could be affirmed of the * Unguiculata * of 

 the Linnaean and Cuvierian systems and summed up, in recapitulation, 

 the following as amongst the more remarkable indications of their 

 affinity to the Oviparous Vertebrata in particular orders or genera of 



