KIN SCHULTE, SEI WHALE. 



of the muscles by connective tissue takes place during foetal life. Carte and MacAlister's 

 description concludes as follows: 



"The inferior or posterior fibres of this muscle ran downwards as far as the lower part of 

 the pouch, and some of them were traceable backwards in the median line, forming a sort of 

 subcutaneous muscular expansion on the anterior surface of the abdomen; this, however, did 

 not expand laterally in the cervical region, and hence that part of the neck external to the inner 

 margin of the sterno-mastoid muscle had no superficial muscular investment." 



They would thus seem to have considered the longitudinal layer an extension of the mylo- 

 hyoid, which is probably to be attributed to the "dartoid character" of the muscle in their 

 specimen and its infiltration with fat making an exact discrimination impossible. The nerve 

 supply would have cleared up the condition, but this they do not seem to have ascertained. 



The redundancy of the musculo-cutaneous complex of the ventral pouch in reference to 

 the deeper structures is a striking peculiarity of this fcetus as contrasted with those of the 

 toothed whales. While as yet no furrows have appeared, we are evidently dealing with their 

 antecedent developmental condition. 



It is to be noted that the extent of the pouch far exceeds the limits of the intermandibular 

 region and is patently in excess of the demands for space incident to the distensibility of the 

 oral cavity, so that Kuckenthal's reference of the throat furrows to this cause alone would not 

 seem to afford an adequate explanation of their presence on the thorax and abdomen. Andrews ! 

 has suggested that originating in the intermandibular region their caudal extension has taken 

 place in correlation with the increased expansion of the thorax incident to the large size of the 

 lungs and the reduction of the sternal fixation of the ribs in the Balsenopterinse, an explana- 

 tion which has the advantage of including a larger number of facts and which accords with 

 the structure and extent of the integumentary complex. The difficulty that meets us here is 

 to find grounds for attributing to the ribs under the action of the inspiratory muscles in life 

 an excursion of such degree as to require and utilize a redundancy of the integuments. Mliller 2 

 has thought that the increased freedom of the ribs in Mystacoceti stood in relation to a lessened 

 degree of diaphragmatic respiration as contrasted with the Odontoceti. In favor of this he 

 finds the greater size of the inspiratory muscles in the former and the diminishing develop- 

 ment of the diaphragm in their older foetuses, in one of which he found a centrum tendineum. 

 But granted that such a distinction can be established between the two suborders, it is still 

 to be shown that it can become quantitatively so great in the rorquals as to require an ampli- 

 fication of the integuments, and it is also a question whether in them the type of respiration is 

 not still predominantly abdominal even though it be so in less degree than in the toothed whales. 

 Hasse 3 has presented much evidence to show that the direction of the respiratory movements 

 of the several parts of the thorax accords with the direction of the corresponding bronchi, and 

 that the degree of the movement is proportional to the diameter of the bronchus. With this 

 in mind the pattern of the bronchial tree of B. musculus, as given by Muller (cf. op. cit. Fig. 39) 

 would seem by the inclination of its secondary branches to indicate an abdominal type of respira- 



1 Andrews, R. C. Monographs of the Pacific Cetacca, I. The California Gray Whale (Rhachianectes glaucus Cope). Mem Am 

 Mus. Nat. Hist., N. S., Vol. I, Ft. V. New York, 1914. 



8 Muller, O. Untersuchungen tiber die Veranderungen, welche die Respirationsorgane der Saugetiere durch Anpassung an das 

 Leben in Wasscr erlitten haben. Jenaish. Zeitsch. f. Naturwiss., Bd. 32, 1898. 



3 Hasse, C. Die Forraen des menschlichen Korpers und die Formandcrungen dcsselben bei der Atmung. Jena, 1888-1890. Bi>- 

 merkungen iiber den Bau der Lungen und iiber die Form des Bruskorbes bei dem Menschen und bei den Saugetieren Arch f \int 

 und Phys., 1893. 



