THE ANATOMY OF THE WEDDELL SEAL. 81 



been elevated. These are the musculus obliquus externus abdominis and the musculus 

 rectus abdominis. Both of these muscles are attached to the pubis, i.e. to the un- 

 yielding or rigid pelvis, and between them they provide slips or digitations of insertion 

 into nearly all of the ribs, even extending to the first. Further, the musculus obliquus 

 abdominis externus has no attachment to the ilium in other words, both of these 

 powerful muscles were pubo-costal in their attachments. With a distended chest and 

 a glottis firmly closed so as to render the chest wall fairly rigid, these muscles by their 

 contraction could clearly compress the abdominal contents ; but in association with an 

 open glottis, of necessity they must pull their rib attachments towards the pubis in 

 other words, they must act as depressors of the ribs and thus as powerful expiratory 

 muscles. Such a depressor action compels one to presume and to accept an elevated 

 position of the ribs during inspiration. 



There is nothing in the mechanism which seems to require one mode of action for 

 inspiration by the vertebro-sternal ribs and another mode of action by the vertebro- 

 abdominal ribs. Of course, the first costal arch, from the nature of its sternal articula- 

 tion, is, even in the seal, capable of less elevation than those ribs whose shafts and 

 costal cartilages are longer and whose sternal articulations permit greater freedom of 

 movement ; but, in order to secure a uniform method of elevation throughout the series 

 of ribs, it is necessary to provide some more rigid line or point d'appui for the start of 

 the movement, and the combination of the first costal arch with the manubrium sterni, 

 together with their powerful scalene and sterno-mastoid muscles, provides such a line. 

 Moreover, in man the clavicle is added to this line by the sterno-mastoid and trapezius 

 muscles as well as by such ligaments as the costo-clavicular and the sterno-clavicular. 

 Again, it will be found that those ribs which elevate most readily are just those whose 

 heads are provided with an interarticular ligament passing between the head and the 

 intervertebral disc. Such a powerful structure would be unnecessary unless there 

 were a tendency for the head of the rib to be drawn away from the vertebral column as 

 the dorso- ventral and transverse thoracic diameters increased owing to the elevation of 

 the ribs in full inspiration. There is no ordinary form of inspiration which requires a 

 larger amount of air under regulated control than the inspiratory movement performed 

 by the trained singer, and one of the approved methods of obtaining this result aims at 

 the expansion of the large dorsal surface of the lungs by cultivating the upward move- 

 ment of the ribs in relation to the dorsal surface of the chest, as being not only easier 

 than, but preferable to, a forced action of the diaphragm. An examination of the 

 mechanism of respiration leads me to the conclusion that, in all forms of respiration, 

 this mechanism acts in the same way, but not, in all its parts, to the same extent, for 

 any particular respiratory act ; that ordinary and laboured respiration differ in degree 

 rather than in kind ; that the degree of respiration depends upon the amount of air 

 required for any particular form of exertion ; that the difference between the respiration 

 of the quadruped and the respiration of man results from differences in their attitude 

 ^horizontal and erect), whereby each cultivates that form of chest movement which 



(ROY. soc. EDIJJ. TRANS., VOL. xLvm., 331.) 



