SCHULTE, SEI WHALE. 439 



left beyond the dome a pyramidal space containing fat. The existence of this space would 

 suggest that the recession of the apices of the lung was due to intrinsic causes, and not primarily 

 to the shortening of the neck or the great development of muscles in this situation. Ventrally 

 are the sternohyoid and sternothyroid muscles; the triangular interval between them and the 

 scalene gives passage to the great vessels, vagus and phrenic nerves, and is covered superficially 

 by dense cervical fascia. The space thus defined though large is no more than adequate for 

 the passage of the oesophagus, trachea and laryngeal sac. Caudad the diaphragm is attached 

 ventrally between the ends of the sixth ribs, thence ascending in the midline to the fourth space. 

 To this ascending slope is attached the pericardium. From the postcava the diaphragm slopes 

 dorsad and caudad attaining its most caudal point at about the middle of the last rib. This 

 division of the diaphragm into two sharply denned planes meeting at an angle, appears to be 

 a fcetal condition dependent upon the unexpanded condition of the lungs. 



Pleurce. The dome of the pleura is lodged in the interval of the scalene-rectus complex, 

 rising high in the first space, but not reaching the caudal margin of the first rib. Here the pos- 

 terior thoracic artery and accompanying vein cross its summit. The reflection of the pleura 

 dorsally follows the margin of the rectus capitis anticus major, overlapping its ventral surface 

 increasingly caudad, and this more on the right side than on the left, to reach the beginning 

 of the descending aorta. From this point the sacs of the two sides are in contact and their 

 reflections cross the aorta obliquely, passing from its right to its left side as they proceed caudad. 

 On the diaphragm they are separated by the pericardial attachment, coming together again 

 upon the ventral thoracic wall and so continuing to the first space, there passing transversely 

 laterad to the posterior thoracic artery along which they ascend to the dome. On account 

 of the obliquity of the diaphragm the pleura extends farther caudad dorsally than ventrally, and 

 reaches farthest caudad in the angle of the diaphragmatic origin, between its attachment to the 

 last rib and its lateral crus. This point is at about the middle of the rib, and is distant 76 mm. 

 from the dome of the pleural. Ventrally in the midline the extent of the pleura is 43 mm. and 

 in the approximate dorsal midline, along the aorta from the beginning of its descending portion 

 to the hiatus aorticus, it is 46 mm. The pleural sacs are widely separated at the rostral thoracic 

 aperture by the great size of the mediastinal complex as it passes into the neck, especially the 

 trachea and the laryngeal sac. A well defined ligamentum latum descends from each hilum to 

 the diaphragm. 



Lungs. The* lungs are long and rather narrow, attaining their greatest vertical breadth 

 at the junction of pericardium and diaphragm, where an angle is formed in the ventral margin. 

 Beyond this they narrow slowly by the retreat of the ventral margin and are abruptly truncated 

 caudad. As the ventral margin turns here to an approximately transverse course a small angular 

 projection is formed, which is the most caudal point of the lung. Mesal to this the margin 

 ascends slightly cephalad before becoming transverse. From the angle at the pericardio- 

 diaphragmatic junction caudad the margin is very sharp and is formed by a narrow fold of 

 visceral pleura, into which pulmonary tissue has not extended and which is translucent when 

 held to the light. The rostral portion of the ventral margin is thick and rounded, extending 

 to the apex with a sinuous course. At the sides of the pericardium it is concave, as is also the 

 mediastinal surface, while rostrad, beyond the pericardium both margin and surface become 

 convex. The dorsal border is thick and massive filling the costovertebral groove. It is straight 

 except at its beginning and end where it curves ventrad to a slight degree. The surface of the 



