440 MK. 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, ii), 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 (h) 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 (t) 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 Eib. 



The third rib (fig. 75, iii) 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 7^. 



It projects freely ventrad and sHghtly postaxiad ; and the tail of its Y has a similar, 

 though less marked, curvature to that of the second rib (fig. 1, in). 



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, convex, 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. 



