1905-6.] On Delphinus acutus from Coast of Sutherland. 313 
spines and the tips of the transverse processes were partly 
cartilaginous. The spinal cord ended opposite the 5th post-costal 
vertebra. 
Twenty-five chevron bodies were counted : the 1st began in 
line with the 20th post-costal vertebra; it and three succeeding 
chevrons were small, and the two lateral halves were not united 
mesially to form a ventral spine. The last chevron was associated 
with the 45th post-costal vertebra; it and the four chevrons 
immediately anterior, though small, possessed each a stunted 
ventral spine. The intermediate chevrons were considerably 
larger and with well-marked ventral spines. 
The sternum, 5J inches long, consisted of three segments, and 
formed an elongated, flattened bone. The manubrium was the 
widest ; its anterior border was recurved and a pair of cornual pro- 
cesses projected from it; the 2nd piece was about half the width of 
the manubrium ; the 3rd piece was narrower and bifid at its free 
end. Five pairs of ribs articulated with the sternum and 
their sternal segments were ossified. From the 6th to the 10th 
rib the corresponding sternal segment was ossified and the segment 
belonging to the rib in front was overlapped by the corresponding 
segment of the rib immediately behind ; in the respiratory 
movements one was permitted to play upon the other. The last 
five ribs were floating and their free ends were tipped with 
cartilage. These arrangements, together with the articulations 
of the last ten pairs with only the transverse processes of the 
dorsal vertebrae, gave great mobility to the chest walls and 
permitted the full expansion of the lungs which takes place when 
the animal dives. The pelvic bones were almost straight and 
slender, 2 ”2 inches long; the ends were cartilaginous. 
The length of the head in a straight line from the occipital 
condyls to the tip of the beak was 14'3 inches (375 mm.). The 
length of the beak from the notch in the maxillary bone to the 
tip of the premaxillaries was 7T inches, being in proportion to the 
length of the head about 1 to 2. The transverse diameter of the 
base of the beak between the two maxillary notches was 3 '8 inches. 
The interzygomatic breadth of the skull was 7 '6 inches. The malar 
bone was a long, very slender style. The two pterygoids met in 
the mesial plane behind the palate, their suture was continuous 
