SEAL-EMBRYOS. 17 



would not have expected is that, in spite of the presence of a large liver, the right 

 lung extends backwards to a greater distance than does the left, thus giving the right 

 lung a greater antero-posterior, as well as a greater transverse diameter. A small 

 lobus impar was present connected with the root of the right lung. 

 In specimen No. 24 the actual measurements were 



Greater antero-posterior length right lung . . 88 '5 mm. 

 Greater antero-posterior length left lung. . . 85 '3 mm. 



CIRCULATORY SYSTEM. 



As in the case of the other systems, the anatomy of the circulatory system of the 

 Pinnipedia has been so fully and carefully described by Dr. Murie (loc. cit.) that there 

 remains but little to add, and I shall content myself by referring merely to a few 

 points which have either been omitted by that author, or which I wish to accentuate. 



The heart appears to be somewhat disproportionately broad, being mainly due 

 to the breadth of the right ventricle. The heart in specimen No. 24 furnishes the 

 following measurements : 



Total maximum breadth . 55 mm. 



Total maximum length ... 50 mm. 



1 light ventricle breadth . . . 35 mm. 



Riorht ventricle length . 50 mm. 



O O 



Left ventricle breadth .... 20 mm. 

 Left ventricle length .... 35 mm. 



The apex is traversely blunted, with a distinct notch separating the apices of the 

 two ventricles. There is nothing in the interior of the heart requiring special mention 

 beyond the fact that there is a well-marked moderator band. 



From the arch of the aorta spring three arterial trunks, an innominate, a 

 left carotid, and a left subclavian, as Murie has shown to be the case in the Otariidae 

 but not in the Trichechidae. There is but a single renal artery to each multilobular 

 kidney. With regard to the middle sacral artery, around the morphology of which 

 so much discussion has centred, I failed to discover, even in quite young specimens, 

 any evidence of a primitive double nature. So far as I was able to determine, this 

 artery was distinctly a median continuation of the dorsal aorta arising at the point of 

 bifurcation, perhaps slightly from the dorsal aspect. In one fcetus (No. 24) the 

 middle sacral took origin from the dorsal aspect of the right common iliac artery, just 

 at its commencement ; I could find no corresponding branch arising from the left 

 common iliac. 



The middle sacral itself, as one would expect from the very reduced size of the 

 tail, is an exceedingly slender vessel. About the distance of a couple of vertebrae from 

 the point of origin it gives off a pair of bilaterally symmetrical branches which have 

 all the appearance of ordinary segmental arteries. 



VOL. V. 



