82 MR. C. W. ANDREWS ON THE SKULL AND 
of the hypotarsus. Lower down the shaft it is narrowed and flattened, its outer 
border being formed by a prominent ridge, which is continued upward and outward, 
and terminates above in the process which forms the outer border of the external 
glenoid fossa ; its inner border is formed by a less prominent ridge, which is not, as in 
Cariama, continuous above with the inner ridge of the hypotarsus. 
The outer face of the shaft is bordered by the ridges which form the outer edges 
of the anterior and posterior faces. This surface widens out towards the middle of 
the bone, and is flat or even slightly concave. The outer surface is slightly convex, 
and is not very sharply marked off from the posterior surface. 
As above mentioned, the shaft is incomplete in both the metatarsi of the type- 
skeleton, but the distal portion (three or four inches) of the right metatarsus is very well 
preserved. The upper portion of the shaft preserved in this specimen is very slender 
and roughly triangular in section, one angle of the triangle being a rugose ridge on 
the posterior surface. A short distance above the inner trochlea, and at the lower 
end of the ridge just mentioned, is the surface for the attachment of the hallux (hal.). 
Below this the posterior surface is slightly concave from side to side. ‘The anterior 
surface has near its outer side a shallow groove deepening distally and having at its 
lower end the foramen for the tendon of the adductor digiti eaterni. This foramen 
leads into two channels, one opening between the outer and middle trochlea, the other 
on the posterior surface of the bone immediately above the trochlee. 
The distal trochlee are arranged in a slightly curved line (fig. 17). The median 
trochlea (tr. 3) is very large and its articular surface is sharply delimited, both 
anteriorly and posteriorly; the median groove is much deeper behind than in front. 
The inner trochlea (tr. 2) is relatively small, and is considerably shorter than the 
middle one. Its articular surface is evenly convex from side to side, except on its 
posterior side, where it is slightly grooved. It is situated a little posterior to the 
middle trochlea, behind which it projects considerably. The outer trochlea (ér. 4) is 
rather larger than the inner and is slightly longer; it also projects considerably 
behind the median, and its articular surface is grooved posteriorly only. The lateral 
surfaces of all the trochlee are deeply excavated by pits for the insertion of the 
ligaments of the toes. 
In comparing the metatarsus of Phororhacos with that of other birds, it must be 
remembered that it has probably been profoundly modified in correlation with the 
loss of the power of flight and the consequently exclusively pedestrian progression 
of the bird. Among the peculiarities which may probably be thus accounted for 
are the simple hypotarsus, the relatively great length of the bone, and the disposition 
of the distal trochlee. ; 
The metatarsus of Diomedea differs in several respects, the chief of which are 
complete absence of all trace of a hind toe, relatively large size of the articular ends 
compared with the shaft, breadth and complication of the hypotarsus, and absence of 
a pit for ligament at the outer side of the base of the intercondylar tuberosity. 
