440 MR. ST. GEORGE MIVART ON THE 
length of the first rib, or even more. Nevertheless its length is to the extreme length 
of the nineteenth vertebra (to which it is attached) only as about seven to six. 
It projects freely ventrad (fig. 1, 11), and is in the form of a Y with very short arms 
and with a curved stem. ‘The stem is, on the whole, rather concave outwards, but with 
a slightly sigmoid flexure. The head and neck of the rib () may be more slender than 
any part except the distal end of the rib; more slender absolutely, and very much more 
so relatively than in the first rib. The head itself has a subcircular circumference. 
The tuberculum (f) is slightly shorter than the neck, but considerably broader, much 
flattened pre- and postaxially, but with a rounded articular concavity at its tip. It is 
very little larger absolutely, and very much less so relatively, than in the first rib. 
The vertebral margin (between the head and tubercle) is strongly concave, very 
much more so than in the first rib. It presents an exceedingly large pneumatic 
foramen (f). 
The ventral or preaxial margin of the rib is more rounded than the dorsal or post- 
axial one. Proceeding distad from the capitulum, this margin is at first gently concave 
and then gently convex. 
The postaxial margin may develop a low, long prominence, with a rounded outline, 
a little distad of the tuberculum. On this account this margin, proceeding distad from 
the tuberculum, is at first concave, then convex, and then again gently concave. 
The Third Rib. 
The third rib (fig. 75, 111) is a little more than twice the length of the second rib; but 
neither the capitulum nor the tuberculum is quite twice the length of the capitulum 
and tuberculum of the latter. 
This third rib bears a proportion in length to the twentieth vertebra (to which it is 
attached) about as 3} to 74. 
It projects freely ventrad and slightly postaxiad; and the tail of its ¥ has a similar, 
though less marked, curvature to that of the second rib (fig. 1, 111). 
The capitulum is relatively rather longer and more slender in proportion to the 
tuberculum than in the second rib; it is the slenderest part, except close to the actual 
extremity of the free distal end. 
The head itself presents a rounded, conyex, articular surface for the parapophysis; 
that on the tubercle (for the diapophysis) is nearly twice the size of the corresponding 
surface on the second rib. Its dorso-ventral diameter slightly but decidedly exceeds its 
pre- and postaxial extent. 
The vertebral margin (between the capitulum and tuberculum) is much more sharply 
concave than in the second rib, forming an acute angle of about 60°; but its pneumatic 
foramen is little, if any, larger. 
The tuberculum seems to continue on in the main and general direction of the rib, 
and the capitulum to diverge obliquely inwards from this. 
