526 
MR. SIBSON ON THE MECHANISM OF RESPIRATION. 
69. The Seal ; great respiratory apparatus. 
The Seal (fig - . VIII.), of all the animals we have yet considered, has by far the most 
capacious chest ; compare its large breathing apparatus and small abdomen with the 
small chest and enormous paunch of the Rabbit (fig. XI.). The chest of the Seal 
admits of very great expansion and contraction. Its slender ribs and very long 
flexible costal cartilages, its peculiarly deep dorsal arch, the great size of its levatores 
costarum, and the development of its intercostals, its external oblique, transversales 
and sterno-costals, all combine to give it very great power both of expiration and 
inspiration. The respiratory development is entirely thoracic, the scaleni having less 
action from the neck in this than in any animal we have yet examined. 
Porpoise, Plate XXVI. fig. VII. §§ 70-77- 
70. The Porpoise has a large portion of lung in the neck. 
The Porpoise, to which we now turn, has a development of respiratory power far 
greater even than the Seal. In addition to the usual thoracic and diaphragmatic 
space for breathing, this animal has a large portion of lung occupying the neck ; in 
this it contrasts remarkably with the Seal. 
The whole build of the Porpoise corresponds with this great cervical respiration. 
Its cervical vertebrae are all amalgamated to form one bone, on which the head has but 
little motion. The first and the succeeding five ribs articulate with long, slender, 
almost bony costal cartilages or sternal ribs, having moveable joints at each extremity. 
The sternum is broad and hollow within. The diaphragmatic ribs are six in number ; 
of these the superior only has a costal cartilage. 
The first rib has, owing to its long double-jointed costal cartilage, very great play 
in respiration. 
71. A peculiar scalenus (1 a.) ; the sterno-hyoid and sterno-thyroid, while they act on 
the first rib and sternum, also expand the lung in the neck. 
The lungs rise up into the neck almost as high as the base of the skull ; they are 
almost surrounded by muscles, having in front very powerful sterno-hyoid (13) and 
sterno-thyroid (14) muscles, and to the side, and behind, a large and very peculiar 
scalenus (1 a.). This scalenus is like the half of a funnel or hollow cone; it arises 
tendinous from the base of the skull, descends, and soon forms a hollow fleshy web 
that increases as it descends, half embraces the large portion of lung in the neck, 
and is inserted into the whole circuit of the first rib, and the costal half of the first 
costal cartilage. There is yet another scalenus to the outside of this, which is much 
shorter and smaller, arises from the vertebral transverse process, and descends ob- 
liquely forwards to the first rib. 
The sterno-hyoid, sterno-thyroid, and large scaleni, all join to complete a circuit 
embracing the lungs behind, in front, and on each side, the vertebrae being, of course, 
behind, the larynx and pharynx between the lungs. When these muscles all act toge- 
