424 DR MORRISON WATSON AND MR ALFRED H. YOUNG 
members of the group, that we find certain observers™ affirming that the only 
exception is formed by the Greenland Right whale (Balena mysticetus), in 
which, as SANpiForT?t first pointed out, the observation being subsequently 
corroborated by Escuricurt and Rertnuarpt,{ the trachea presents the 
peculiarity of “being only bifurcated into two bronchi, that branch, which 
in other cetaceans (and several land mammals) issues from the trachea before 
its bifurcation into those two bronchi, not being found here.” There are, how- 
ever, among the cetacea two other exceptions to what, in respect of the sub- 
divisions of the trachea, may be called the usual arrangement. We refer to 
Pontoporia Blainvillii, in which Dr H. Burmeister § describes and figures a 
trachea which, previous to its bifurcation, gives off two accessory bronchi which 
pass, one to the right and the other to the left lung. A similar arangement has 
been described in Monodon monoceros.|| Another interesting but less remarkable 
deviation from the usual arrangement was found by CArTE and MAcAtIsTEr 1 in 
Balenoptera rostrata. Were the three-fold bronchial arrangement exists, but 
the accessory bronchus, instead of coming from the trachea prior to its bifurca- 
tion, is given off further back than usual, and thus becomes an offset of the 
right principal bronchus. Balenoptera thus presents an arrangement inter- 
mediate between that of the exceptional Greenland Right whale and that met 
with in the majority of the cetacea. Beluga, then, in respect of the respiratory 
organs, agrees with the greater number of cetaceans, and differs only in the 
relatively greater length of the trachea. JIrregularity of the posterior tracheal 
rings, and incompleteness of those situated next the larynx, are met with in 
most cetaceans. The annular form of the intra-pulmonic bronchial cartilages 
is likewise common throughout the order. 
CIRCULATORY ORGANS. 
Heart.—The heart is broad, and, as usual in cetaceans, is somewhat 
flattened from above downwards. Its length from base to apex corresponds — 
to its basal breadth, the measurement in each case being 6 inches. The 
auricles are capacious, and possess large appendages. Internally, the walls 
of the auricles are for the most part quite smooth; each appendix, on the | 
contrary, is provided with numerous well-developed trabecule carnea. 
These consist of fleshy bands, which, attached to the walls of the heart 
by their extremities, are free in the middle. They are not arranged in — 
the regular, pectinate manner so common in the mammalian heart, but 
cross one another in all directions—those of the left side being more 
regularly disposed than are those of the right. The cavity of the right 
* IL p. 265; XVIL p. 236, + XXIV. p. 245. t XX. p. 103. 
§ XXV. p. 484. || XXVI. p. 139. GL p. 243, 
