1881.] NATURAL SCIENCES OE PHILADELPHIA. 135 



dissection was onh^ a day old, it was important that the heart and 

 blood-vessels in a more fully developed animal should be examined 

 with reference to determining whether the circulation was in any 

 way modified by age. 



On opening the thorax of the animal it appeared to me that in 

 both sexes the heart was large in proportion to the size of the 

 animals. This is in a great measure due to the thickness of the 

 walls of the left ventricle. In the female Hippopotamus, which 

 was the first examined, I suspected this might be due to hj'per- 

 trophy, but finding it to be the case in the male also, perhaps 

 this is normal. The heart, in an empty condition, measured, 

 from base to apex, 9 Inches, and in circumference 14 inches. The 

 wall of the left ventricle measured 1 inch in thickness, that of the 

 right ^ of an inch. According to Gratiolet,^ the heart in the 

 young Hippopotamus terminates in two points, the ventricles 

 being separated by a little groove, reminding one of the form of 

 the heart in the Manatee and the Dugong. There was no indica- 

 tion of this groove in either of the Hippopotami examined by me. 

 With the exception of the absence of the corpora arantii on the 

 semilunar valves of the pulmonary artery and their very slight 

 development in those of the aorta I did not notice anj^thing 

 peculiar about the interior of the heart. The aorta gave off the 

 coronary arteries first, which were very large and then an innomi- 

 nate and the left subclavian. The innominate divided into the 

 right subclavian and a trunk which bifurcated into the two com- 

 mon carotids. The external carotid as well as the ascending 

 cervical and occipital arteries were all rather slender vessels in 

 proportion to the size of the head and neck. The external 

 carotid artery was very much larger than the internal. A pecu- 

 liarity about the external carotid artery of the Hippopotamus first 

 described by Gratiolet,^ I noticed m both the male and the female 

 animals, the fact of the vessel in its course towards the head 

 passing between the hyoid bone and the digastric and stylo-hyoid 

 muscles in such a manner that when the hyoid is elevated the 

 vessel is compressed against the bone by these muscles. The 

 effect of this disposition is that the blood is cut off" to a 

 great extent from the brain and head when the animal sinks 

 under water, the hyoid being elevated at such times. Gratiolet 



^ Recherches, p. 358, and Planche III. 

 2 Op. cit., p. 354. 



