288 ZAGLOSSUS. — 
OSTEOLOGY. 
In their original description of the Proechidna Peters and Doria (1876) 
figured the imperfect cranium on which they based the species. The adult 
skeleton was next described and well figured by Gervais (1877-’78) in the first 
part of his Ostéographie des monotrémes. Dubois (1881) has figured the skull 
and the bones of the limbs, and in a later paper (1884) the elements of the 
sternum. He also gave brief notes on the skeleton. Thomas (1885, 1887, 
1907, 1907a) has given cranial measurements of specimens in the British mu- 
seum, and Weber (1888) has figured and described other adult skulls. The 
present discussion is confined to a summary of these notes together with such 
additional observations as I have been able to make on three other adult skele- 
tons and the skulls of five younger specimens. 
Skuuu.— The cranial sutures close early, and by the time that full size 
is attained, they have become nearly obliterated, although the other bones 
of the body are still incompletely ossified. Adult crania are therefore practi- 
cally solid like those of birds, except that the ring-like tympanic bones remain 
separate from the rest of the skull. The seven crania in the collection of the 
Museum of Comparative Zodlogy represent several stages in this progressive 
ossification from that in which nearly all the sutures are evident, to that in which 
all have disappeared. The homology of the several bones, owing to the difficulty 
of obtaining specimens young enough to show the sutures, is still somewhat 
unsettled. Sixta (1900) endeavored to homologize the cranial elements of 
the adult Echidna with those of certain reptiles but van Bemmelen (1900) showed 
that this was only possible after a study of young skulls. The latter author 
and Lubosch (1906) have written on the monotreme skull and appear to have 
elucidated the main points. Our Proechidna material, however, seems to 
throw additional light on a few doubtful questions, and presents other details 
of value. 
The occipital and parietal regions of the brain-case are most developed, 
a condition which Gregory (1910) notes as primitive among mammals. The 
exoccipitals are large; the dorsal and lateral margins of each are nearly at 
right angles where they meet dorsal to the condyles. The large supraoccipital 
slightly exceeds in breadth the combined width of the exoccipitals, with which 
it forms the posterior face of the skull. There is considerable variation in the 
degree to which these three bones share in forming the superior margin of the 
