THE ANATOMY OF THE WEDDELL SEAL. 75 



the first to the fifteenth. Its fibres were directed obliquely backwards towards the 

 ventral mesial Hue, 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 interims 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. 

 Each 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 a/ygos 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 i Id ailed 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, 

 i.e. erect, as in the case of man. 



(ROY. SOC. EDIN. TRANS., VOL. XLVIII., S'2.''.) 



