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XVII.—Scottish National Antarctic Expedition: Observations on the Anatomy of 
the Weddell Seal (Leptonychotes Weddelli). By David Hepburn, M.D., C.M., 
Professor of Anatomy, University College, Cardiff (University of Wales). Part III. 
(MS. received March 28,1912. Read June 3, 1912. Issued separately July 18, 1912.) 
THE ReEsPiRaATORY SYSTEM, AND THE MECHANISM OF RESPIRATION. 
In the specimen under consideration there were fifteen pairs of ribs, of which nine 
pairs were vertebro-sternal. The costal cartilage associated with each of these was long 
and very flexible. The articulation of the first pair of costal cartilages with the sternum 
was effected by means of a short but strong band of fibrous tissue, which permitted 
considerable freedom of movement and did not form a junction of the more or less rigid 
character seen in man. 
The chondro-sternal joints of the second, third, and fourth costal arches were of the 
diarthrodial variety, each joint being divided into two separate cavities by an inter- 
articular ligament. The fifth, sixth, seventh, eighth, and ninth chondro-sternal joints 
presented diarthrodial joints without interarticular ligaments. 
The sternum was long, narrow, somewhat like a four-sided rod, and divided into 
seoments (suggestive of vertebral centra) by amphiarthrodial joints which were 
placed opposite the chondro-sternal joints from the second to the ninth. A suprasternal 
tapering cartilage extended towards the head for a distance of two inches, while the 
ensiform cartilage extended backwards to a similar distance and ended in a broad semi- 
lunar expansion. 
The intercostal muscles were well developed, being thick and fleshy, presenting little 
or no, fibrous intersection. They were arranged so as to present an external and an 
internal muscle in each intercostal space, and the direction of their fibres was similar to 
that seen in man; but the fibres of the external muscle were continued between the 
costal cartilages close up to the margin of the sternum without the intervention of an 
intercostal membrane. 
The triangularis sterni muscle arose from the deep surface of the sternum on its own 
side of the mesial plane. It consisted of a number of slips, which were wide enough to 
give the appearance of a complete sheet of muscle. These were attached to the sternum 
from the level of the third costal cartilage backwards to the level of the ninth. The 
fibres ran forward and outwards to be inserted into the deep surfaces of the costal 
cartilages from the second to the ninth inclusive, and into fibrous bands which passed 
from one cartilage to the other. The general line of insertion into the costal cartilages 
was near to the series of costo-chondral joints, each of which, except that of the first rib, 
TRANS. ROY. SOC. EDIN., VOL. XLVIIT. PART II. (NO. 17). 49 : 
