OSTEOLOGY. 295 
closely applied along the symphysis for some 40 mm., are not anchylosed, but 
doubtless remain separate throughout life. The measurements of three adult 
skulls and two smaller and more youthful examples, as well as those of the 
type as given by Peters and Doria (1876) are tabulated on page 296. Thomas 
(1888) gives dimensions of two skulls in the British museum. 
Gervais (187778) in his account of the osteology of this animal figures 
two skulls. The first is shown in his Plate 9, fig. 1, of natural size, and is of 
almost exactly the same dimensions as M. C. Z. 12,415 given above. No sutures 
are indicated and it is doubtless the skull of a nearly mature animal. Gervais 
considered it the skull of a male. In his Plate 7, figs. 1-1b, are shown three 
views of a larger skull, of natural size, which if correctly drawn, indicate a larger 
animal than either of the old examples here noticed. The greatest length of 
the skull, as measured from these figures is 197 mm.; basal length, 187; palatal 
length, 174+; tip of rostrum to orbit, 129; least interorbital width, 19; great- 
est width of brain-case, 57; anterior margin of orbit to temporal canal, 43; great- 
est length of mandible, 153. 
The hyoid apparatus of the Proechidna appears to be still undescribed. 
The larynx is situated far posteriorly on the throat and the hyoid bones are 
few and small (Plate 2, fig. 7). The basihyal is relatively broad and bears at 
each end on its anterior face a cephalic cornu of two pieces, the basal of which 
probably represents a ceratohyal. The more distal piece is of about half the 
size of the latter and tapers to a point which is connected by tissue with the 
sides of the pharynx. No tympanohyal articulating the larynx with the skull 
appears to exist. At the posterior face of each end of the basihyal, a large thyro- 
hyal passes dorsally to the cephalic cornu of the thyroid cartilage. The cricoid 
cartilage joins the thyroid by a common median cartilage, though a faint trans- 
verse line probably indicates the original separation of the portion proper to 
each ring. The more ventral portions of thyroid and cricoid are bony. The 
arytenoid processes are produced backward as a long tapering cartilage to the 
dorsal end of the cricoid. Following the cricoid is a large, nearly complete 
tracheal ring, succeeded by the trachea, which consists of some 18 or 19 carti- 
laginous pieces not quite complete dorsally. 
VERTEBRAE.— The vertebrae of the Proechidna have been well figured by 
Gervais (1877—78) and their general character is asin the Echidna. The first 
seven (cervicals) have a complete vertebral arch, formed by the union of the 
cervical rib with the transverse process and the centrum. In old individuals 
these ribs become solidly fused with their respective vertebrae. Such true 
