536 PROF. ST. GEORGE MIVART ON THE 
for articulation with the coracoid. In the middle of the preaxial end of the sternum a 
groove proceeds obliquely ventrad and preaxiad, and may end preaxially in a deep fossa. 
The costal angles (ca) are much as in Struthio. The postaxial margin of the sternum 
has one median and two external xiphoid processes (ma & lx). There is no prominence 
in the wide, more or less deeply marked, concavity which extends on each side of the 
median xiphoid process. 
Each lateral margin of the sternum is slightly concave. 
The pleurosteon is not so wide dorso-ventrally as in Struthio. It bears five articular 
surfaces for the five sternal ribs. The fossee between these surfaces are not nearly so 
deep as in Struthio; and each pair of superimposed articular surfaces are not so plainly 
convex, and not even relatively so much separated from one another. 
If we eliminate the keel, then the sternum of Pelecanus is much like that of Struthio ; 
but the angle made by its coracoid groove is most nearly approached by Casuarius of 
all the Struthionide. The concavity on the ventral surface of each costal angle is 
somewhat deeper than in Struthio. 
SULA. 
The skeleton of Sula is shortly described by Mr. Eyton in his ‘ Osteologia Avium,’ 
p- 220, with the figure of the entire skeleton (pl. 61). Of this genus I have examined 
the following specimens :—a disarticulated skeleton in my own collection ; a mounted 
specimen in the Museum of University College, Kensington; six specimens (1189, 
1185 a, and 1186 a—p) in the Museum of the Royal College of Surgeons; and three 
specimens (Nos. 527 6, 731 a, and 779 a) in the British Museum. 
The total number of vertebra seems to be generally forty-three or forty-four, without 
counting the pygostyle. 
These vertebre are subdivisible as follows :—fifteen cervical, three cervico-dorsal, and 
six dorsal (the above numbers are constant in all the specimens examined); the 
lumbar vertebra are generally three, but they may be two or four; the lumbo-sacral 
vertebre are generally three, but they may be only two in number; there are one or 
two sacral vertebre; the sacro-caudal and caudal vertebre, taken together (and 
excluding the pygostyle), are generally twelve, but may, rarely, be as many as thirteen 
(of these the seven last are caudal). 
The whole axial skeleton, when compared with that of Pelecanus, is of a more 
compact and dense texture, and less pneumatic. The various ridges and processes are 
thus sharper and more marked. The styloid rib-like processes are more conspicuous, 
being free and not merely forming part of the side of a subcentral groove. 
Metapophyses are much more developed; but hyperapophyses are not so; while, 
except in the second, third, and fourth vertebree, where they are much larger, median 
hypapophyses are still less developed and little more than rudiments, save in the 
seventeenth and eighteenth vertebree. 
