THE ANATOMY OF THE WEDDELL SEAL. 329 
the first to the fifteenth. Its fibres were directed obliquely backwards towards the 
ventral mesial line, and, having given place to a thin aponeurotic sheet, many of these 
fibres interlaced with those from the opposite side to form the linea alba. 
The hinder part of the muscle, however, did not form any attachment to the ilium, 
but as a muscular arch, equivalent to the ligament of Poupart, they were attached to 
the ventral aspect of the body of the pubis. Near to the pubis a slit in the muscle 
sheet served the purpose of an external inguinal ring, in which the spermatic cord was 
situated. A muscle so attached could clearly act as a very powerful expiratory muscle 
provided the glottis were open. 
The musculus obliquus abdominis internus was attached dorsally to the lumbar 
aponeurosis and to the crest of the ilium, while ventrally it was inserted into the hinder 
borders of the last four ribs and also through its aponeurosis into the linea alba. The 
greater proportion of its aponeurotic fibres passed ventrally to the rectus abdominis 
muscle along with those of the external oblique, but a few of them blended feebly 
with the aponeurosis of the transversalis abdominis muscle. This muscle (transversalis) 
presented lumbar and iliac attachments as well as a series of digitations on the hinder 
seven or eight ribs. Its mesial attachment to the linea alba was by an aponeurotic 
sheet placed on the deep side of the rectus abdominis muscle. The hinder or inguinal 
margins of these two last muscles were very closely, almost inseparably, blended 
together, and both were much thinner than the external oblique muscle. 
The rectus abdominis muscle occupied an abdominal sheath whose composition has 
already been indicated. It was attached posteriorly to the body of the pubis, and 
extended anteriorly to the first costal cartilage, to which, as well as to all the other 
sternal cartilages, it was attached by tendinous slips. Here again we can see that this 
muscle, acting from a rigid attachment to the pubis, may act as a powerful expiratory 
muscle in association with an open glottis. 
The lungs, beyond what has already been said, do not call for detailed description. 
Hach presented a great oblique fissure, and thereby an apical and a basal lobe. In 
addition the right lung possessed a transverse fissure, and therefore a middle or ventral 
lobe. Furthermore, the right lung had an azygos lobe on its mediastinal aspect in 
relation to the margin between diaphragm and pericardium. 
On several occasions I have had the opportunity of making a detailed examination 
of the respiratory mechanism of mammals whose habitat is either partly or entirely 
marine, and on each occasion I have been impressed by the remarkable flexibility of 
their thoracic wall, with the associated peculiarities in the attachments of certain of the 
muscles. Attention has already been drawn to some of these peculiarities in the 
descriptions given above, and it is almost impossible to avoid the conclusion that 
respiration necessitates a more flexible chest-wall in the case of mammals surrounded 
by water than in those which are surrounded by air, apart from the fact that the 
normal attitude of the latter may be horizontal, as in the case of quadrupeds, or vertical, 
v.€. erect, as in the case of man. 
