ON THE EPtSlERNAL APPAEATUS OF MAMMALS. 563 



perhaps to the median piece of Coelogenys and Cavia, in which its 

 relations are the same as in the Pinnipedia. 



In the Monotremes, again, as in the Lizards, transverse processes 

 reappear coincidently with the presence of clavicles. These struc- 

 tural arrangements recur in the Opossums, as has been formerly- 

 shown in detail, in a more rudimentary form, the parts long retaining 

 their cartilaginous condition, and presenting in the other species 

 provided with clavicles various grades of development. In the 

 above-mentioned Marsupials the clavicles are no longer superim- 

 posed upon the transverse processes of the T-shaped piece, but are 

 connected with their extremities only, and this constitutes the usual 

 relation of these parts in all the remaining and higher species of 

 Mammals. An asymmetrical median piece of the episternum no longer 

 appears, as in Coelogenys and Cavia^ for the two connate pieces 

 at the anterior extremity of the manubrium sterni in Dasypus 

 novem-cinctus do not appear to me to be correctly referred to the 

 azygous piece of the episternum, but to correspond rather to the 

 symmetrical pieces. In other species, as in Dasypus sexcinctus, the 

 separation or division of the symmetrical pieces is well marked, and 

 here the bony pieces of the episternum annexed to the sternum are 

 connected, with the clavicle on each side by a long ligamentous band 

 of union. To the same category belong the structures that have 

 been above described in Mies and other animals in which there is a 

 ligamentous union between the episternal and clavicular bones. The 

 connection with the sternum is, however, of a much lower character, 

 both in the Hodentia and in the Insectivora. In these orders two 

 parallel series occur. In Sorex, as well as in Mus minutus and M, 

 musculus, points of ossification appear in the cartilaginous epister- 

 nals, whilst in the Hedgehog and the Hamster the episternals re- 

 main completely cartilaginous, articulating in both with the clavicle. 

 Finally, a reduction in point of size occurs in Scmrus, together with 

 absence of articulating cavities, and even in the Mole there is only a 

 partial development of an articular cavity at the clavicular extremity 

 of the episternals. The arrangement observed in Monkeys and in 

 Man occupies an intermediate position between these several forms ; 

 for, on the one hand, on account of their small size the episternals 

 are here allied to those of Scmrus, and on the other hand, by the 

 development of articular cavities they acquire a resemblance to those 

 of other Rodents. 



From the foregoing considerations, then, it would appear that 



