334 MR. W. K. PARKER ON THE OSTEOLOGY OF BAL^NICEPS REX, 



was one of these free hsemapophyses on the right side with the rudiment of a second 

 near its tip ; whilst on the left side there were two such bones, the anterior piece 

 being very long, passing downwards more than an inch behind its homotype of the 

 pelvic rib, and upwards of an inch behind the rib itself. A structure this well worth 

 noticing, bringing us, as it does, so near to the condition of these parts in the Crocodile. 

 In the Puffin {Fratercula arctica), and in the genera Alca and Uria the posterior ribs 

 and hsemapophyses are prolonged so far backwards that the very angular articulation 

 of the last or pelvic nearly reaches as far back as the tip of the very long and slender 

 OS pubis. 



Sacral and Caudal Vertehree. (PI. LXVI. fig. 1 sc, cd ; & PI. LXVII. figs. 2 & 3 5C, & cd.) 



The first two sacral vertebrae are almost as large as the dorsals, and their boundaries 

 are very distinct ; they then rapidly decrease in size and in distinctness ; yet the next 

 four are indicated by their short blunt pleurapophyses, the last two of which scarcely 

 reach the ilium. The stunted pleurapophysis of the right side of the second sacral is 

 not anchylosed to its parapophysis. After the first six, the next five sacrals have their 

 extremely small pleurapophyses confluent with the sides of the centrums, without any 

 out-standing part. The remaining six sacrals have out-standing coalesced pleurapo- 

 physes, the second and third of which are extremely thin, and are principally composed 

 of threads of diploe. The neurapophyses of all the sacrals except the last have in this bird 

 completely coalesced. Between the first and second sacral there is a large oval foramen 

 for the exit of nerves, but it is much less than the passage formed in the dorsals between 

 the neurapophyses of contiguous vertebrae. The posterior and anterior roots of the 

 spinal nerves have separate outlets in the rest of the sacrum ; and from these passages 

 to the roof of the pelvis there is a large quantity of very rich diploe involving the sub- 

 stance of the neurapophyses, neural spines, diapophyses, and pleurapophyses. The 

 neural spines of the sacrum are at first equal to those of the dorsals, but between the 

 acetabula they spread, become rounded, and then obsolete. There is in this, as in 

 most birds, a large triangular space for the insertion of the dorsal muscles on each 

 side the sacral spines ; the roof of this space is oblique and is formed by the ilium ; the 

 floor is horizontal, and consists of the diapophyses. 



Looking at the pelvis from above (PI. LXVII. fig. 2), there may be seen two pairs of 

 small passages between the spine and the iUac bones, just as these large bones begin to 

 divaricate before they turn outward on each side towards the acetabula. Behind these, as 

 the spine gains breadth but loses height, there is a deep fissure divided by oblique septa on 

 each side of the spine ; these septa are the diapophyses of the middle part of the sacrum. 

 The iliac bones become further and further apart ; and where they join the coalesced 

 dia- and neur-apophyses, four pairs more of oval passages, most of them quite small, 

 indicate from above the boundaries of four more of the sacral vertebrae. Two additional 

 pairs of large transversely oval openings or interspaces, the anterior pair of which is 



